you know, a couple days after this "rally," it will all be forgotten. i think you're making a mountain out of a molehill. you have a good paying gig. if you don't do the gig, you won't. my first obligation is to my family above all else. the truth is nobody really cares what your political leanings are and after this event, they'll resume not caring.
otoh, if this is a nambla or nazi rally, they WOULD care, and i wouldn't do one of those gigs under any circumstances. but if it's just your average run of the mill political thing, do the gig and forget about it, as everyone else will.