Yeah, if you suck then it's pointless.
But plenty of people do things simply because they enjoy it. Not because they see it as a ticket to a non stop unicorn parade.
Approaching random hotties on the street (or anywhere you come across them) can be a FANTASTIC way to have fun, that doesn't cost a nickel. So long as you don't care what happens, and see it ONLY as having fun, it's a great way to slowly expand your social skills.
Even somebody like Dave could find ways to have fun with playful openers:
Hi, my name's Dave and I absolutely suck with women. I'm definitely NOT trying to pick you up, because if I was I would have passed out from terror right now. I'm just trying to improve my social skills by talking to gorgeous women. So, uh, what's your favorite color?