I am a shorts guy as well, but for many situations pants are better. They protect from the sun, they protect your legs from getting cut up if you need to bushwack or hike on an overgrown trail (seriously, you can get lacerations on your legs from "trails" in some places), they protect your legs from poison oak, poison ivy, stinging nettles, thorny plants, ticks, mosquitoes and they are much, much more durable than long underwear. Long underwear tear super easy, running tights are much better for hiking in.
My issue with pants has been finding a pair that fit well. They are all just way too baggy (I'm skinny) on me or too tight around the waist. Maybe I will just save up and buy a pair of outlier pants.