More importantly, I think you argument only works if you look at the "future generations" as a series of unborn children and not as literally the entirety of future humanity. A better analogy would be to say that climate change activists should be against the abortion of an entire generation. The scope of the costs renders a clear difference to the abortion of some individual fetuses.

This part doesn’t make sense to me. It seems like you’re saying that since an individual abortion doesn’t affect humanity much (although you admit aborting an entire generation is problematic), people should be allowed to abort babies. Analogously, since an individual using plastics indiscriminately doesn’t affect climate change much, people should be allowed to use plastics however much they want.