I think alcohol works better as a counter-argument. In Germany, it is not only legal, but it is also legal to sell in 'bubblegum flavour party boxes', obviously aimed at children. It is legal to sell at checkout, so after a recovering alcoholic is tired out by all the shopping they can be tempted by a little bottle of vodka or whatever.
Despite this, and a social culture that revolves around drinking, the vast majority manage to avoid serious alcohol problems.
This essentially shows how responsible people are - even with a culture that makes it very easy to start, and very difficult to quit, most people manage to maintain a reasonable distance from an extremely addictive drug.
If you follow this argument along, I think if you legalized drugs, but also put some restrictions on their use (for instance, not allowing supermarkets to sell them, not allowing child-branded stuff, etc) - there's no reason to imagine the situation would not improve vis-a-vis the current one.
All this said, my preferred drug policy (for all drugs, including alcohol) would be something like a ban on their public use and sale. As somebody who used to take a lot of drugs, I have no illusions about the destabilizing influence they can have on people's lives. Alcohol is well known for being a force multiplier for pre-existing misery or mental instabillity, and I think even mild drugs, like weed, work in the same way.