UV filters though degrade image quality. Why buy nice glass just to put a “protective” filter on it that gets in the way of the image?!
The real concern is decentering the lens by dropping it, but no filter will protect it from that.
I've been saved by an ND0 filter when I bashed the lens against a rock. It destroyed the filter's screw thread but the len's wasn't damaged.
I also once while whale watching got 'steam blasted' by a humpback whale that exhaled while scratching it's back on the boats keel. I was able to quickly unscrew the steamed-up filter and carry on photographing.
Edit - This is also why I religiously use the lens hoods - if nothing else they form a sacrificial protector.
Clear filters can’t hurt IQ other than introducing flare or ghosts in backlighting. It’s possible to crack or scratch your front element with minimal to no effect on your picture; a clear piece of glass isn’t going to do anything.
Or causing fringing, or reducing sharpness, or reducing contrast...
The absolute _best_ that a filter can do to IQ is nothing. But that's basically impossible. Every air/glass interface causes reflections, and no piece of glass is optically perfect. So it's going to hurt your IQ, the question is merely how much, and whether it's worthwhile.
I used to use them. Then I decided I was probably never going to get much of anything reselling my lenses, so I might as well just use them instead of trying to baby them. Haven't had a problem with that decision, but YMMV.