"You get a bunch of people hanging out high"

Doesn't that assume though that the "bunch" is a bunch of the same size?

I would argue that the bunch will become larger that is that more people with a predisposition will get hooked on the high.

Of course we don't know that number. Could be 1% higher could be 20% higher. Compared to the other societal costs people might judge it to be a fair tradeoff. Or not.

Mostly true, but you will still have some of the negatives you mention, just as we do in relation to alcoholism. That's not a reason to maintain prohibition, but if we're making drugs legal then we should channel some of the tax revenue to harm mitigation, which is inevitably going to be necessary.

Alcohol is legal and not high cost. So either alcohol is different from those drugs (if so how?) or its very similar, which means this drugs will have the same ills as alcohol.