When bro is such a bro you completely forget he's trans.
My wife's got a friend this happens with all the time. She'll be talking to him and something about our oldest will come up. She'll make some remark to him thinking he'll relate, entirely forgetting that he had to transition so he didn't experience whatever it was the same way.
Unnecessarily doing it especially to a newborn should absolutely be illegal. Sometimes it might be medically necessary, like my son opted to have it done years ago because he was entirely non-retractile and it was causing him a great deal of pain. But outside of instances like that? Shouldn't be done.