Church? Auditorium?

I got another announcement today regarding members of the Washington Symphonic Brass playing a brass and organ concert this Monday evening. I skipped their last concert because I knew some of the music, Carmina Burana in specific, to be blatantly secular, and all of the venues were dedicated church sanctuaries.

I perceive that very few Americans feel concern with the performance of secular music in a dedicated sanctuary. Even moderately conservative Christians, such as the conductor of my college symphony, feel nothing wrong with performing music of, for example, Gershwin, in a sanctuary.

Why do I see this as a problem?