And toothbrushes too, did you know in some countries it is legal to brush your teeth and buy a toothbrush even if you didn’t see a dentist in the last year?
I'd love to see some facts backing this up. It might be true that wearing slightly off prescriptions could train eyes slightly worse over time, but for most people going without them is a far worse option.
Also, the skillset required to prescribe glasses and contacts is something that can be (and is in some countries) effectively on the job training, not necessarily something that requires a specialist doctor with years of education. In most of Europe your average glasses shop can put you in a machine for a few minutes, and spit out an accurate prescription.
Medical regulations exist for the good of the public, and I wouldn’t risk treating a condition that a medical professional’s diagnosis is required for. The FDA would only block self-treatment if it were dangerous.