I've watched documentaries about why people do it or ask to have it done to their babies, and as far as I can tell, it's a combination of brainwashing and the fact that people think it's just what you do if you have a boy. Like there are people out there who either don't know about any reasons why, they don't really see any point but they get their son done just because other people are getting their babies cut! I kid you not! Now that there's more info about circumcision out there people know there's no health, medical or cosmetic reason for it to be done, but they assume the majority of boys are cut and so they get their son cut just because of that!
I've watched youtube videos about why Americans had their children cut, often the first baby is cut out of ignorance and was done because the doctors asked, and they had no reason to question anything doctors or nurses said to them, and figured because the doctors and nurses brought it up then maybe they should, they'd never seen one being done and didn't know what it is (although I've seen some mothers telling other mothers to get it done *but don't watch it because it's traumatic*) and often choose not to get future sons cut, because they lost the fights with their husbands/families, or they just assumed that it's what you should do for no reason other than it's a "normal" thing to do. a lot of videos were done by mothers discussing why they chose to have it done to their sons, and what baffled me was that while in many cases the mothers had no idea what they or their sons were in for or what was being amputated, many were educated, but claimed that facts that would have changed their mind were things they didn't know about. For some they said they didn't realize it could kill their son (yeah, really - how that could be true I'll never know; common sense says any surgery can kill), they didn't realize the majority of boys born now are intact, they didn't realize there was no point as far as hygiene goes but they did know about the sensitivity loss and the reduction in sexual function (yet still decided to go ahead with it!). But the most common reason seems to be that a circumcised penis "looks better" of all things.
But I actually don't really know why people actually go through with it. Sure, being able to say you have a belief that something might be better is very different to me to actually going through with such a heinous procedure. I'm still wracking my brains working out why someone I know not only had it done to her children (didn't stop after seeing the horror show after first) but wanted it done to my child! At least where I live (Australia) it's not the done thing, it's very rare to have it done to a child, and hospitals flat out refuse to do them. I shudder to think what someone in a similar situation in the US could do to protect her child.
The worst thing about a society where genital mutilation has been so common is that society as a whole loses understanding about the genital parts which are often removed - people don't see them in real life, they don't understand what they do, a lot of people don't talk about what it's like to have it, and when it comes to foreskins they've been demonized to a huge extent. A lot of people talk about how "gross" or how much smegma stinks, and they really have no idea what they're talking about - obviously if you'd seen/smelt it you wouldn't think that let alone say it. People don't know how sex is supposed to be. all the negative effects of circumcision are considered "normal" and people half the time don't even know these issues are caused by circumcision or even think they could be.