My hubby has never really been into porn. He has watched it with friends, but doesn't bring it into our house, and certainly understands why I don't get into it.
For us it's a matter of respect and that includes self respect. What does it do to a relatiponship when you have to hide things about yourself out of fear of upsetting your spouse? It isn't a good thing whether you're hiding porn, over-spending, or anything else you know they don't approve of.
I think saying it's a "guy thing" is just an attempt to justify it. Not all guys are into it, and those whose wives aren't, need to respect her feelings as well if they expect to keep her happy. It's kinda sad to think anyone would risk a relationship for a fantasy.