What I think:
1) Circumcision is largely an issue of cultural (including religious) norm. People then rationalize this norm by saying that a circumcised penis is cleaner and healthier.
2) Circumcision for medical reasons (phimosis, mainly) has been overdone. Boys who had no issues with their penis (no discomfort, no infections) were (and still are) subjected to painful procedures and/or circumcision because physicians had decreed that their foreskin should be retracted before a certain age.
3) The reluctance to let nature take its course for foreskin stretching may be related to the fact that the foreskin is eased by erections and movements resembling masturbation, which was taboo, thus physicians were likely more inclined to suggest circumcision to worried mothers than "just let him play with himself, ma'am, and it will ease out".
4) Circumcision (especially "high and tight", I think) may make masturbation without lubricant uncomfortable, especially if done by partners, or even cause difficulties in intercourse.
5) Circumcision in the United States was initially motivated by the fight against masturbation (see point 4), and was then rationalized again for hygiene and for reduction of venereal diseases.
6) While circumcision reduces some venereal diseases due to unprotected sex, it does not reduce them considerably; using condoms is a must in any case, which defeats the purpose. It only makes sense for that purpose in cultures where wearing a condom is difficult (e.g. some African countries).
7) While circumcision helps in keeping the penis clean, it is insufficient. Sure, there won't be smegma, but it can still taste of pee and sweat. One has to wash in any case. Again, this defeats the purpose, except perhaps in areas without adequate hygiene.
8 ) The insistence of surgery for phimosis before, say, age 6, may be motivated by a desire of not having to deal with objections from the boy. I don't quite like this attitude from physicians.
9) Many women have a curiously casual approach to the topic, as though circumcision had no adverse effects (but see point 4). Some even find the topic humorous. It shows that this is not their genitals that are cut.
10) If phimosis was so much of a problem that so many boys have to be cut, then certainly it would have been a problem before circumcision became massively applied to "cure" it in the 19th century. Yet, we don't read of masses of men in European countries in the 18th century - early 19th century having notable health problems due to phimosis. There are some limited exceptions (it is said for instance that Louis XVI of France had to have surgery before being able to have complete intercourse with his wife Marie-Antoinette due to a tight phimosis), but certainly, given the masses of boys circumcised due to "phimosis" in the late 20th century, we should have heard more about such issues.
In short, if one could predict at birth that a boy will face severe phimosis later on, that's not amenable to natural stretching, then I'd support circumcision as a newborn, but since this cannot be predicted at this stage, then I think this is just abuse.
Nobody in the Western world would think it appropriate to remove the prepuce of the clitoris for better cleanliness in infant girls, or to remove the hymen (when not imperforate) of infant girls because it might help them someday with intercourse, or, as AGracier says, to allow parents to have their baby tattooed. But we allow acts more permanent than a tattoo.