There are principles at stake, but there are also tactics to consider. What is this particular boycott likely to achieve?
Well, strangely enough, I think that a union not well known for its political effectiveness to call for a boycott with no means to enforce it, that does not have overwhelming support amongst either its members or its delegates to Council, which affects only a very small number of its members, which gives Israeli academics an opt-out if they just say they don’t like what their government is doing very much, and so bloody on and so bloody forth, is unlikely to achieve very much at all.
It might, just, generate another Mona Baker / Andrew Wilkie cause célèbre. (I’m not sure we need another of those.) It’s unlikely to do more. And I don’t think it’s terribly likely to get the Israeli government or electorate to change its mind about the Occupation of the West Bank and Gaza.