Kawa - I'm so, so sorry. That really was not fair for him to act that way, however, I have heard it is a common reaction. I read this blog once (I think I found it on the circumcision board) by a guy who said what it was like for a man to be presented with this information, although factual, may make the man feel like what you are saying is that his penis is inferior, not doing a good job, etc. They can't help but take it personally, even though it wasn't their choice. It's also coming to terms with that, too. It was something done to him without his consent and there is nothing he can do to take it back. He may not even realize that either. The fact that your older boys are circumcised probably doesn't make him feel like is something you believe in as you wouldn't have done it to your older boys. Now, a rational person (and one that has BTDT in the sense of trusting 'others' around you) would know that this is NOT brought on by hormones, but instead by education. It's really that simple. He may see you apologizing to your older boys and again, taking that personally as well. Like something is wrong with him.
It may take time and like you said, this is an issue that isn't just going to go away. I do understand the need to be on the same page with him, though, so you won't ever feel like you are fighting against him about the issue. I hope it gets better soon!