I think the problem is that Matt has become even less tolerant of gay people since RW and he realizes most of the world has becomes more tolerant. I think he knows that if he were honest about his feelings, he would be attacked by his roommates, viewers, etc. and he doesn't want to bring that harassment/negativity into his or his family's lives. So he doesn't want to talk about it on camera at all.

There's no reason Matt can't be Christian and accepting toward gay people. Plenty of Christians are (like the church Danny helped re-roof). But clearly Matt belongs to church that isn't accepting of gays and he believes in that, too. He's just trying to keep his mouth shut to protect himself from backlash.

As far as being gay, maybe he is, maybe he's not, but he'll never let his mind go there enough to find out because he's so terrified of the possibility. It's sad.