harms: squinting, headaches, fatigue, etc

also debate about whether not correcting vision leads to worse vision in still developing eyes

It depends on the activities you're engaging in! Let's say a person is slightly near sighted with a prescription for 20/40 vision. If they're driving, I'd definitely recommend wearing their prescription, otherwise the likelihood of accidents is increased. If they're at home, reading a book with sufficient light, they don't need to wear their prescription as there is minimal to no potential harm. (See. https://en.m.wikipedia.org/wiki/Visual_acuity)

On the plus side, depending on the type of company one keeps, glasses can be aesthetically pleasing!

Harmful: Stepping or tripping on things you can't see. LEGO bricks are painful!