I recommend reading the multiple pages of information on the Birth website, or from any non-biased source.

I am anti circumcision, but DH is done and said he would want his son/s to be done to look like him. I chose not to make an arguement out of it at the time (I wasn't even pregnant when he said this), but chose to read up on the matter once I became pregnant. I read a book, and I searched the net, including videos on YouTube, so that I had a good defence. Then, instead of confronting DH about it and getting all flustered like I do when I argue, I emailed him asking that he please read the facts on the Birth website, and if he still wanted to do it then we could discuss it, but otherwise I'd assume the issue had been dropped. Thankfully he's never mentioned it since. He's probably also noticed that I've joined a couple of anti-c groups on Facebook, and realised I wouldn't be a walkover on this issue!

So in short - research, research, research!