I'd figure those plastics wreak havoc in the long term in an individual life but won't prevent people form reproducing and developing. It might be a serious setback but just a hurdle for humanity. Climate change, our nuclear arsenal, ... pose more urgent threats.

Curious why you've got two emojis in your username?

Pretty sure plastics save more.lives than they destroy. Modern medicine isn't nearly as effective without them.

I wouldn't necessarily be convinced of that. I'd put that in a similar category as climate change. It might catastrophically ravage the world, but I think humans would survive. It's not the same punctuated event as nuclear fission. If a crazy person got control of nukes early in, they could wreak havoc on the world. Initial blasts kill tons of people, radiation would likely not be fully understood and fallout changes the global landscape before humanity can realistically react. Contrast that with global warming and microplastics, we know (we as in humanity in the broader sense) these are issues. It might need to get to the catastrophic ravaging before enough people are convinced, but eventually it will happen. And the intervening time won't cause humans to go extinct. Sure billions might die, but not all.