In my personal belief, everyone[0] has the right and moral obligation to fight the injustice they care about at the level they can manage. If that's handing out water at the protest or inventing penicillin, do what you personally can do to improve the world.
[0]the average layperson, obvious exceptions for power/money apply
The only reasonable argument for drug legalization, in my opinion, is the libertarian one - the idea that you should be free to take the drugs you want to take. I am sympathetic to this argument. I am someone who is able to make wise decisions about the drugs I take. But I also recognize that millions of my fellow citizens are not. The harm to society from drug addiction and overdoses outweighs the benefit to me getting high whenever I want.