First, there are antisemites, a tiny minority. Second, there are those like Greta Berlin (and Henry Norr and others), who consider antisemites who support Palestinian liberation to be valuable voices, demand their inclusion, defend their legitimacy, and challenge refusal to tolerate them misguidedly as "silencing." This tolerant attitude towards bigotry is the most likely cause for Berlin's mistaken tweet. Third, there are the majority of Palestine solidarity activists, who don't care for the support of bigots, and consider their inclusion and especially, giving them any prominence, the kiss of death. The board of Free Gaza, to which Ann Wright belongs, appears to have firmly planted its feet in the second camp by the tenor of their response, which dismissed the controversy as a non-issue and rejected criticism, crucially criticism by some of the most respected and longstanding Palestinian activists, as illegitimate.
There are many reasons why a person would defend bigots. Of course, the most damning reason comes immediately to mind: he or she could indeed approve of their bigotry. This possibility cannot be dismissed, and inevitably it casts a shadow over people. But there are other less damning reasons as well. He or she could be genuinely unable to recognize the bigotry. Because bigotry does a great part of its harm by being normalized, not being able to see it is a form of de facto support and complicity, even when it is not purposeful. Thus, it is not an excuse, and people who cannot see bigotry must be challenged to learn to see it.
Finally, she or he may clearly see the problem, yet believe that this particular bigotry should be ignored in a particular case for reasons of a political urgency and expediency. "Utilitarian" debates of the last type are quite common. It must be noted that there are many cases where almost every leftist would consider that is it legitimate to work with people who hold political views that one abhors. To take the most extreme but well known example, the radical left-wing militias fought together with the extreme right-wing ones in the Warsaw Ghetto uprising. To take a more pedestrian example, imagine a group of workers striking for pay while expressing bigoted positions on other questions, such as immigration: most leftists would support the strike. A closer example was the support many on the Egyptian left gave to the Muslim Brotherhood in the recent elections in Egypt. Thus, this last reason is indeed one that cannot be dismissed in principle and require serious attention, by evaluating context, situation and form. A key difference is between ad-hoc interactions, and sharing a single organization in which bigotry is normalized. The second is in principle never acceptable to leftists.
However, a prerequisite of debating how to respond to bigotry is the ability to see the difficulty and the costs, and to debate them rationally based on shared political assumptions. Those who cannot recognize antisemitism (or use a minimizing definition of it that is rejected by the vast majority of people on the left), and read rejection of bigotry, falsely, as an unacceptable challenge to "freedom of speech," rather than a matter of a fundamental political difference, do not fit the last category. That means that they fit in one of the other two. And that is the problem.
With regards to the Estelle, the matter is complicated by the circumstances. On the one hand, Wright was denied participation. There is no reason to deny someone participation in an action for the offense of not being clear or holding a minority opinion, beyond the minimal requirements that the group defines as its points of unity. It would be a mistake to start making stringent conditions on participating in political actions.
On the other hand, the Estelle is a small boat going into a potentially life-threatening situation. In this situation, trust is paramount, and those on the boat have a legitimate reason to carefully selecting whom they allow on board. Wright, as member of the FGM board, is responsible for the board's handling of the scandal, which included responding to respectful criticism by close colleagues with challenging the legitimacy of raising concerns. According to the statement of the former board members:
Consultations and efforts made by some of the former members of the board with the current board members were either rejected or set aside, which has added to our disappointment.
To this, the board responded by characterizing all those who took issue with them, including the approach of the former board members, longstanding and respected Palestinian and solidarity activists, "vicious attacks." In doing so, the board effectively described fellow activists and the Israeli media are one and the same and asked the broad movement to treat them in the same way. This is the Ann Coulter strategy and the word for this is bullying, which is compound in this case in that the context is the Palestinian liberation struggle and some of those bullied are Palestinians engaged in that struggle for decades. On this background, the decision of the Estelle is understandable. People who respond to criticism by bullying the critics are dangerous to their friends, and could be deadly in the kind of situations that the Estelle might meet.
Furthermore, the mission of the Estelle is to bring attention to the plight of Gaza under Israel's siege. Since much of the impact depends on coverage, one assumes the tenor of the media coverage that the boat gets is of paramount strategic importance to participants. Having on board a person who would lead media attention on a tangent would be detrimental to the mission even if that person were impeccable. This is not, after all, about Wright, and she has no right to expect that the people on the Estelle jeopardize their mission in order to "prove" that they don't consider Wright an antisemite. Wright says that she was disinvited "due to allegations of anti-Semitism of the Swedish Boat to Gaza by pro-Israelis groups in Sweden." Crucially, the Estelle did not publish their decision. Instead of recognizing the fact that her presence at this time would not be in the best interest of the mission, Wright effectively launched a public attack on the Estelle, paraphrasing what she was told in a way that suggest the organizers are subservient to Zionists. Again, this is the Ann Coulter strategy, and it should be condemned. Most likely, the boat organizers don't want to spend their limited resources defending someone who made herself a liability by her own disregard of fellow activists. They are right to privilege their mission, and Wright's subsequent behavior only justifies them further.
Norr's intervention is another example of bullying, and one that is furthermore built on abusing language. "Guilt by association" is a logical fallacy that consists on drawing a conclusion about one person based on an a non-essential similarity or relation with another. For example: Stalin is a communist and a mass murderer. Therefore other communists are guilty of (or support) mass murder. Or: The Occupy Movement was praised by a Neo-Nazi, therefore the Occupy Movement has a Neo-Nazi problem. These are fallacies. On the other hand, when people willfully associate with each other, in speech, writing, or through formal association, their association is indeed reflective of their politics. This is not "guilt by association." It is common sense. If a party in the US issues a statement defending or denying Stalin's crimes, the leadership is not victim of "guilt by association". It is simply wretched. If a person repeats defining elements of Nazi arguments or rhetoric, it is not "guilt by association" to point this out. It's a true indication of where they are on the political map. There is a rule of thumb most people master by the age of 16. You shouldn't associate with people you don't want to be associated with.
So far, nobody has accused Ann Wright of anything (except me, here, of trying to bully others to shut up). She is certainly not "guilty by association." It is Norr who is guilty of loose, uncalled for language. Berlin (and others) are also not victims of "guilt by association." They are however responsible for who they associate with, especially when those association lead to damage to others, and should not be surprised if those associations cast shadows over their credibility. They are also guilty of not understanding, or pretending not to understand, that political work is carried out in associative form, and therefore the freedom of association is its primary freedom, of which the freedom not to associate is an essential part. They seek to deny the rest of the movement the freedom of association by bullying others, with their language of "witch hunt", "guilt by association", and "sheer madness," into association with bigotry that they reject.