Re: AIDS: here is what the AMA has to say: "...behavioral factors are far more important risk factors for acquisition of HIV and other sexually transmissible diseases than circumcision status, and circumcision cannot be responsibly viewed as "protecting" against such infections."http://www.ama-assn.org/ama/pub/cate...int/13585.html
I.e. if he practices safe sex, being circumcised adds no appreciable benefits; if he doesn't practice safe sex, he'll be at high risk for HIV and other STDs, whether he's circumcised or not. So leave his foreskin alone and resolve to teach him good responsible sexual behaviors as he grows up.
See also NOCIRC's brochure on HIV and circumcision:http://www.nocirc.org/publish/11-HIV.pdf
As far as UTI's: UTIs in baby boys are fairly uncommon, e.g. a baby boy has a 99% chance of NEVER having a UTI, whether or not he is circumcised. UTIs can be effectively treated with antibiotics, just as they would be in a circumcised boy or a baby girl. Also, breastfeeding decreases the chance of UTIs by a factor of three.
In general, when people bring up medical rationales as an excuse to circumcise, you can point out several things:
1) the potential benefits do not clearly outweigh the risks, harms, and losses of circumcision
2) there are less invasive and destructive ways to obtain the hoped for benefits
3) aside from UTIs in infants, most of the medical rationales given for circumcision do not apply in infants, i.e. it is not something that HAS to be done at birth, rather it is something that can be decided by the male in question when he is old enough to weigh to pros and cons for himself.
Make sure your husband knows the risks of circumcision, the functions of the foreskin, and the fact that no medical organization in the world recommends routine infant circumcision. Also, make sure he sees a video of a circumcision, so he knows what is actually done to a baby. Links to all of these have been posted here a lot, so I won't dig them up right now.
Ask if you need anything in particular, or if he throws out any other reasons. We've pretty much heard them all, and there are answers for anything he can come up with.
Welcome! I'm glad you're doing your research so early in the game.