What you actually said, Jim was:

I do know that falsetto is not natural to men and in order to produce it in young boys to make them choristers (or to train them for opera) it was once practice to castrate them

And that's not entirely true. It's perfectly possible for most, if not all men to produce a falsetto voice. Some high tenors cultivate it as their regular singing voices as it enables them to sing in the female alto range. Yodelling involves alternating between falstto and regular voice. I can produce a falsetto without straining my voice but it only has a range of a major third. It's still occasionally useful to make singing at the top of my range easier in certain circumstances.

Of course it's often used for comic effect.

In the past castration was used to preserve the voices of boy trebles with particularly fine voices at a time when women didn't sing professionally. Given the risk of infection at the time it was very risky and only a minority actually then had a succesful singing career.

They wanted to castrate Haydn but his parents refused. It's as well they did refuse.