Despite having had repeated tonsillitis as a kid (and bronchitis at the same time - unheated boarding school with abysmal hygiene and dozens of boys to a room is quite the disease incubator), my mother, a nurse, dug her heels in, and said no. She'd had to deal first-hand with the outcomes of botched tonsillectomies a few times too many.
They did my brother seven years later without their permission - and he suffers from severe allergies to this day. I have none.
I’ve always been extremely sceptical of “its vestigial” or “that body part is bad for you”. I mean, surely if either were true, selection would have done away with it. If having tonsils were a dysgenic trait, nobody would have them.
I can tell you why it remains such persistent practice - it’s a quick and easy surgery in most cases, and it’s billable at a decent rate in most places. A surgeon in the UK can do ten or more in a day, at £3k a pop. You have an endless supply of patients, and parents who’ll consent because after all they had theirs done when they were kids.
Play your cards right and you’ll make millions a year.