I think the usual argument is that the program costs something to run, and was designed with the assumption that returns would not actually be 100%. Any return

I think the usual argument is that the program costs something to run, and was designed with the assumption that returns would not actually be 100%. Any returns beyond the planned level mean that the program is underfunded, and thus potentially unsustainable. It's also generally considered bad for illegal activity to be allowed to continue. Separately, it's not clear the bottles illegally being returned for deposit are increasing the recycling rate. The article I linked suggests that they are being scavenged from recycling bins, and that (possibly as a result) collected glass recycling in an Oregon-adjacent county in Washington was down 9% after the deposit went up.