If two guys are hanging out and one says “hey I think I think I should take more drugs” and the other says “hell yeah brother do it” they aren’t responsible if the first guy ODs

They are indirectly responsible. Dangerously close, depending on circumstances, of being criminally responsible.

I mean, aren't they? In a moral, ethical, and social stance, don't they share in the blame?

You mean that if you convinced somebody to do something stupid...and then they did it and died...you wouldn't feel guilty at all?

Depending on the circumstances, yes, that would totally be illegal.

It's called "aiding and abetting". In most countries it's illegal to convince someone to do something illegal.

If you are someone the victim sees as an authority figure (especially if the victim is a minor), a bunch of other other charges can be added too.

In Canada, the UK or the USA, for example, someone who "aided or abetted" someone to commit a crime can be punished exactly as if they had committed the crime themselves.