Well we don't know If microplastics are really bad. Let's just assume they are mildly toxic. Since the high amount of children on earth it will still be millions seriously affected.

Well, start with BPAs. Then add PFOAs (ie goretex, jackets are cca pure plastic). Micro/nano plastics themselves are still unknown, but those first two have already caused some significant damage. How do you count rate of cancer X raised by some tiny % Y on hundreds of millions of kids, billions if counting longer timescales since plastics were old news even in 80s?

If you think eating plastics is fine, feel free to start chewing some of it daily, of course lowest quality and price.