I dunno... that choir has sung at inaugurations and similar events for both parties. It's always had elements of being a victory lap, sure, but for a long time it really was a celebration of things like the peaceful transition of power, and that really is something to be celebrated. Also, if you have a precedent for accepting the invitation when it's given, and then you decline because a certain person was elected, that seems equally partisan, but just in another direction. Maybe the solution is to go back in time and not accept any invitation at all, I dunno.
I actually agree with a lot of your point, but I'm uncomfortable with the extent to which you're suggesting our actions have to be governed by what others think, especially when we go on record as to saying why we are doing something. I might be hypersensitive to it now, but one of the things in our political environment that really gets under my skin is the mentality of "you say you think X, but I [somehow] know you really think Y, and Y is bad, and I'm gonna judge you the same as if you had said you think Y". So, apologies as I've probably misinterpreted what you were saying. IMO it's good to be sensitive to perception, but only to a point. If there are naysayers who will pick at whatever you do, and won't believe what you tell them anyway, letting them overly influence what you end up doing seems like a bad idea.