If I throw it in the trash, I know it's at least going to go to a well-managed landfill and has a negligible chance of ending up in a river somewhere overseas, and then into the ocean.
Plus, the feedback feels more accurate. The feeling of how much non-degradable trash I'm creating hits viscerally when I throw plastic in the bin, and makes it hurt more to buy plastic.
I end up using the recycling because my flatmates get angry when I don't.