I read u/AtlasBarfed's point being that we don't have a proper way to put a price on the externalities.

To your point, onerously high taxes could largely remove plastics from the waste stream, mooting the need to determine the cost.

I'd like to go even further. Incentives and prizes and grants and whatever-it-takes to find alternatives. eg Bulk pills in plant-based baggies, instead of monthly oversized labeled bottles and caps.

Nudge the culture and expectations. Every little bit would help. Because better is better.