OP is saying most of the harms come from illegality.

I'm pointing out that alcohol causes immense harms despite being legal, so likely other drugs too would still cause considerable harms when legal (even though yes, it's likely some, like cannabis, would be less harmful than alcohol almost no matter what total consumption settles on under legalization).

I was not arguing about why things are legal or not, only challenging the assertion that drugs aren't very harmful when legal.