Tvad, I respect your opinion and usually agree with most of what you have posted here on Agon. I STAUNCHLY defend our First Amendment rights, no problem with that. But the issue I see here is difference between artists playing their ususal repertoire - political lyrics and all - versus taking advantage of a paying audience and, in essence, doing the old "bait & switch" and digressing off into using the stage as a political soapbox to further their own personal agenda.
I am sure most of the audience already knows the artist's political views - so why do they need to hijack the concert? If you hire me to fix your plumbing or represent you in court, you don't want to hear (nor have you paid to hear) me go off on my own political agenda. Yes, you may listen to me and decide to engage me, but that is YOUR option and decision. I would venture to guess that the majority of the paying public, and that would include many of the fans that are politically aligned with any group or musician, would prefer to hear the songs and music they paid to hear rather than a sermon they didn't. Just my $.02