Depends where in the world you are. In the US it was popularized by Dr Kellogg to curb masturbation. He also recommended a few drops of carbolic acid applied to young girls clits to damage the nerves and avoid what he called "abnormal excitement".

Dude was opposed to pretty much anything even vaguely resembling pleasure, he invented corn flakes as a food to be as bland and tasteless as possible. The only reason they ever became a popular breakfast cereal is because of his brother adding sugar to them despite Kelloggs objections

'cleanliness' and 'looking like their father' were later justifications after the practice had already gained traction.

This is so screwed, too.

Like, I was once tasked to explain to my nephew how to properly clean a penis at, like, age of 7. C'mon, parents, what are you there for?!

Just literally teach it alongside cleaning every other body part, what's the issue? Why should another man show this in particular to your kid?

This doesn't make it justifiable, but circumcision goes back a lot longer than our culture has existed. If Judaism had won out instead of Christianity, it could have been even more widespread than it is now. Some Muslim sects also mandate circumcision, and they could be the ones ruling the world.

Unfortunately, circumcision is a particular form of mutilation that transcends cultures.