>But generally nobody pays quants to lose money. They expect value over the other opportunities they have to use that same money. Is this really controversial?

As with your other comment, this has nothing to do with what the original parent comment was remarking on. They didn't claim, nor did anyone else, that proprietary trading firms weren't making money and that people weren't well compensated due to helping firms make money. Their remark was that the value these firms are providing to society is questionable and that the highly intelligent employees could likely be providing greater value to society elsewhere.

Your comment comes off as "people pay, therefore it has value." Which the inverse would need to be true in that case.

But you are conflating money and value. As you stated, raising children produces value, and as you imply, this is not generating revenue. Which you are also conflating exchanging money with generating value. Sure, liquidity can generate value but don't confuse these things.

People seem to be forgetting that money is a proxy and that a proxy is not the same as the thing you are proxying.

Money and value are different things.