To me, this is a problem that needs broad solutions and some of those solutions are available immediately and some require broader changes, i.e. there are some things I can control and some things I can't.

Living your life in a way that is conscious of these risks and minimizes them when possible makes the avoidance of plastic an ongoing concern, and increases awareness of the issue in public consciousness.

I don't see how broader changes are possible without growing awareness, and often the best place to start is in one's own life.

If you were to examine the decision in a vacuum and discard all downstream effects, I think it's rational not to invest effort if it won't make a difference.

But I think this overly constrains the possible effects of making the changes that we can, and underestimates the value of instilling ideas in public consciousness.