It's not the fault of capitalism but our oversimplified version of it. Externalities such as pollution are not properly included into the price of things. Plastic trash in the water should have been a tiny cost on every bottle and plastic bag. That money could go to whatever resolves the problem (authorities chasing polluters, cleanup/recycling, ...).

In the end, a transaction should leave everything balanced i.e. the buyer gets his soda and the seller gets his money AND (this is the part we are currently missing) every party not involved in the transaction is unaffected, so the environment can't be worse because A bought soda from B.

What we try to do now is regulate capitalism by e.g environmental reuglations and so on - but far from enough, and it doesn't stand a chance of becoming enough as long as it's local efforts in different countries. Large international organizations (OECD, WTO, EU, UN, ...) really need to get this into agreements.

It IS my business if free flimsy plastic bags are allowed in supermarkets in China, whether antibiotics are given to healthy animals in the US or Denmark, or what fertilizer Polish farmers use. The question is what I can do about it? In some cases I can just not sponsor it (e.g. not buy Danish pork) but what do I do about plastic bags in China?