Yes we cut of hair and fingernails. And it is no big deal, easy to agree that it is a reasonable thing to do, even for our children, for several reasons.
First, doing so causes no pain. They are parts of the body that are shed off, no nerve supply, no blood supply, your body expects to lose them as part of the normal wear and tear of living.
Second, they have little value. They give us a chance to make a fashion statement, but beyond that, their value is pretty minor. Everyone recognizes this.
Third, for some people, in some situations, there are clear benefits to cutting them off. Safety issues, hygiene, the time needed to take care of them if left to grow, etc. Ever have a fingernail break off and bleed?
Now consider foreskins. They are not the same at all.
First, the foreskin is a highly enervated, blood vessel supplied part of the body that does not shed off with wear and tear. Instead it is integral to your body and removing it hurts like hell, based on how babies react. Unbearable pain.
Second, the foreskin is highly valuable. Perhaps some would debate this, but I do not think any reasonable person would. Highly important to sexual function and feelings. For both partners. Once you accept the value, then the whole comparison crumbles into dust.
Third, while some may feel that there are some benefits to removing their foreskin, this is highly debatable. Unlike nails and hair, one needs to carefully analyze the trade offs, to make sure that the benefits of removing this highly valuable and integral part of the body justifies the costs from the negative consequences.
There is a better comparison that they could have used. Compare removing the foreskin to removing the tips of their fingers to prevent nails growth and having to deal with cutting their nails. So much easier. So much cleaner. Solves so many problems that can arise, like ingrown nails, broken nails, etc. People do that with cats, so they stop growing their claws. Simple, doable. Why don't people just do that?
The answer of course, is that we value the finger tips and nails. For good reason. And we should do the same for foreskins.
Regards