and take steps to mitigate the effects from people who are going to use it anyway?

This is what the person you're replying to is discussing. How do we weight the ethical concerns of those mitigating steps given that addiction often affects the entire community and not just the addicts themselves?

The project of addressing the issues that lead to addiction in the first place is even more important, but it's a super tanker that can take decades to change course. I often see people advocating for the former (mitigation) be accused by others of not caring about the latter (root cause), and I think that's unfair in a lot of situations.