nails grow back (like hair)

foreskin doesn't

That's quite a big difference

Be more like organs (like tonsils, or appendix) or parts of you body (like part of a finger or earlobe) that you don't really need.

With nails and hair, while there is something alive where the growth happens, i.e. the hair follicle and equivalent for the nail, the bits we can see are dead and have no nerve endings so it doesn't hurt to cut/trim them. The difference from the foreskin couldn't be greater - the foreskin is very much alive, at least while still attached, and has a higher density of nerve endings than most of our skin, possibly exceeded only by our finger tips.

Then as BJade points out, hair and nails grow back. If you've had a hair cut and then thought whoops! that was a bit short, then time will fix it. If you get circumcised and then think it was better before you can't go back. There is restoration but that isn't quite the same.

Seems like something Americans would tell their children to cope?

To be fair, I don't think a lot of American boys are that bothered and, for them, one doesn't need things like this. On the other hand, if someone is angry about it, there isn't really any reasonable response to that and this attempt at downplaying the significance is pretty lame.

I love foreskin, but this is a dumb take

Uhhh. I’m not circumcised but if I was to get it snipped off it wouldn’t grow back like a nail…

Your fingernails and toenails are skin appendages, they grow because the skin of cells are constantly rejuvenating underneath the cuticle and the old cells are constantly pushed out towards the tip of the finger or toe.

Foreskin cell rejuvenate and shed and this is what smegma comes from, but proper cleaning can help prevent the build up of dead skin cells