As someone who needs their glasses for vision correction, it irks me when people without vision problems wear non-prescription glasses. Would you use a walking stick too? Or hearing aid even if you have good hearing? No, you wouldn't.
Yes, it's fine to wear non-prescription glasses. Many celebrities also wear clear lens glasses just for fashion. If you like how they look (or if your eyes need protection from the wind), then go for it. You can wear what you want to. It's a simple fashion accessory, not a false appendage or a gimpy leg as some have likened it to.
Why not? Just do as what you like to do. Wearing clear lens classes is just like wearing ear rings or bracelet. Also glasses with clear lens can protect your from dust, and even radiation from computer.
Of course you can. If you have perfect vision and you do want to wear glasses just for fashion, you can get non-prescription glasses which is also called clear lens glasses. I've seen many people wear clear lens glasses for fashion purpose.