If we legalize drugs, we will remove one barrier to their availability. When we remove that barrier, more will be consumed. The idea that they'll be "taxed and regulated," and thus safe, is baloney, though frequently peddled baloney. They'll be as taxed and regulated, and as safe, and as far removed from use by people too immature to handle them, as "taxed and regulated" booze is now. If you want to see how much that is, sneak into any high school party where the parents are away for the weekend.
Strict libertarians support legalization, and not limited to pot. This is a growing belief in the academic world where I spend part of my time. They are good-hearted people, but too captured by ideology. They think legalization will bring freedom. This is what it will actually bring.