If you want to learn more about the problem, here is an excellent article.

http://toothwalker.org/optics/filterflare.html

As I like high contrast and sun shots the cheap UV filters I brought were a disaster, lots of flare. SSince 2007, none of my lenses have filters and as you would expect the IQ has greatly improved.

As for using them for protection, my old walk around lens EF-S 17-85 received a 3mm long scratch at the edge of the front element. I now always put the lens cap on when not shooting.

Life is about risk management.