Agreement and something to think about
Like Jess, I also bristled at the suggestion that "we play music that we think our audiences want to hear" and I agree completely with her post below addressing this topic. I would, however, like to add that as performers we shouldn't adhere to tradition for tradition's sake. In fact, programming modern music may very well be in our economic best interest.
Increasingly, the traditional model of funding classical music through the philanthropy of little old ladies is proving unsustainable. As these aging donors die off they are not being replaced because younger philanthropists have many more charitable options than existed 50 years ago and are more likely to donate to those causes they find most interesting. If we don't make classical music more interesting to younger generations it will no longer be able to fund its own existence. One of the ways that we can continue to engage younger audiences is through the programming of works that exhibit some relevance to modern experience. In his day Bach didn't have to compete with Jimi Hendrix, Metallica, Green Day, what have you, but in the present day he must! So, if we are to maintain the "classical" music idiom as a museum of the common practice music we must subsidize Mozart through the programming of modern music. True, this will usually mean playing a pops concert, but wouldn't you rather challenge yourself and your listeners by giving them something substantive, current, relevant, interesting and engaging? Personally, I would rather spend my time on Xenakis than on Hoagie Carmichael--but that's just me.
You, as a performer, have a responsibility to educate your audience. They aren't going to demand what they do not know, but when you open their eyes to something new they will remember it. The more we can impact audiences in new ways, the more likely they are to support us. We need to stop seeing modern music as a nuisance and begin seeing it as a path to our continued relevance and job security!