I personally don't listen to any Christian bands, as I typically avoid them. This has nothing to do with the music, as I'm sure there's plenty of talented Christan bands but I just don't agree with the pro-christian message etc. To me, this isn't any different from an average person being turned off by bands with a Satanic image and lyrical themes, or NSBM etc.
I do think it's stupid to argue that "Christian metal sucks" or that there isn't such thing as Christian black metal (for example). It's not a genre of it's own, but a tag to distinguish between them and the typical black metal band, and it's convenient for people who exclusively follow Christian-themed metal, obviously...
I agree with ShredHeadJHJ also. Christian lyrics can co-exist with any genre/style of metal, as can any lyrical theme. I really hate, especially in black metal, when people try to pass the genre off as some sort of pure art form and above any other genre, where seemingly every single aspect of the music is full of meaning and the idealogy/meaning is at the forefront of the music. Sure music is art, expression etc but at the end of the day it's just music.