Why did our music teacher tell us?

They are called "Castrati" and were more closely associated with religious music than opera.

Are you sure that you missed your teacher saying "..like a castrati....", or "..as if he had been...." - and inference from his voice, rather than a statement of fact?

If your teacher actually said this, it wasn't only false, but kind of inappropriate if you ask me. Besides, unless his three kids were the result of artificial insemination or immaculate conception, I think it's safe to assume that MJ was not a castrato.

I know that in the past, some Opera singers had castration done in order to preserve their voice as you say. But MJ, hmmm don't know.

Saying he was castrated would have saved him from the sueing issues regarding the child molestation abuse, and I think he would not have been able to produce ***** to create their children (although he could have frozen it before castration, so it's no proof of that).

LoL maybe your teacher is just trying to look like a know-it-all, something like that would have been a very big scoop in world and entertainment media.

As much as I hate having to say this - his Father just may've been greedy enough to have had this done to Michael Jackson. After all, he was the family's primary "Cash Cow" due to his immense talent & vocal range. Big money will buy you a lot of silence - especially since (as you pointed out, it is barbaric AND Illegal to do such a thing these days) a Dr of some sort would've been involved. Such a person will presumably NEVER tell...
It's not like other Showbiz families haven't financed things like Breast Augmentations to help "boost" the careers of their under-aged daughters - is it? It's all distasteful.
Whatever the truth - I have no idea why your Music Teacher actually told you...

Sounds like she was talking out of her arse....