If you ever happen to meet someone who throws away Lego (rather than giving it away as next years presents or passing it on to various kids/cousins/neighbours kids/etc.) then by all means give them a good whacking for adding to humanity's plastic waste.
But Lego is one of the few bits of plastic that I've never heard of people throwing away. Maybe the occasional piece that gets broken, but even then I certainly remember having more then a few broken bits in my Lego box back in the day... So if people dont throw it away, it cant be counted as waste right?
Biting the hand that feeds IT
