I mean, you realise that legal over the counter heroin used to be a thing, right? Cigarettes are still legal. There is a gap between “obviously harmful thing is legal” and “it is ethical to make great piles of money out of selling the obviously harmful thing (to children, at that)”. The CEO of Phillip Morris, say, isn’t doing anything illegal, but they are a _bad person_ who is knowingly harming society. Same for Zuckerberg.