Well, the umbilical cord is natural, but you don't propose keeping that on, do you? Sometimes there's extra skin, so you cut it off. No harm done. And tooth decay is natural, but I wouldn't advise anyone to stop the unnatural practice of brushing their teeth. A lot of painful, unnatural things (like vaccine injections and life-saving surgery) are actually good for you. So I don't buy the argument that unnatural = bad.
Um, I don't support female circumcision. And circumcised boys/men do clean themselves, just like everyone else. Most humans bathe on a regular basis, yes? It just takes a little more effort for uncircumcised men to keep themselves clean enough to avoid infection. I'm sure they manage to do it, it's just easier for guys who are cut. Maybe because cut men are always clean, as opposed to uncut men, who are only clean right after they shower. I'd hate to catch an uncut dude at the wrong time of day, like first thing in the morning. Hello, buildup. Ick.