What the guest singer includes in his sets for the evening is his/her affair. Nobody is asking YOU to sing the songs. If you don't like the sentiments expressed you can always put your fingers in your ears.

I'm a Greenpeace supporter and I sing songs about whaling and sealing. Why? It's the working conditions that the songs describe-conditions which in 2011 are, certainly in Europe and North America, barely conceivable. Oh, and counter-balance things, I've rewritten 'Davy Lowston' as an anti-sealing song- just in case I encounter a PC audience.