Note that the post explicitly mentions asking the venue contacts whether this is a clear-cut issue, and receiving an answer «it’s complicated». Three days before the conference, I cannot fault the risk-avoidance reaction. Note that interpretation of the clause has settled under German politics of a decade or two ago, not US politics.
I do see some people that have marginal connection to the actual technical work in the project on both sides. However the majority of arguments (representing, in my opinion, the whole range of arguments) are from people who have made technical contributions and care about the project. That doesn’t make me believe some of the claims make sense (I myself don’t buy that the project of this size does, should, or can have a community unified by values as opposed as people-working-on-it unified by scoped technical interests…), but it does make me believe in good faith.
Impact of fundraising decisions on other fundraising and on non-monetary contributions inherently includes political considerations. At the very least, it includes considerations of political reactions of actors contributing.