Don't we all. There should be a rule that says "any non-designer can draw something that he himself can't improve upon".
I'm certainly not arguing in favor of hiring for the sake of hiring, and freelance-everything is how I see the future.
But saying anyone can do anything if they just think about it hard enough is a bit of a stretch. "Jack of all trades, master of none" is real. An actual designer will save you lots of time.
Additionally, there is value in dialogue; having someone to talk to about specific problems helps immensely. And who's going to take time to talk with you about minute details of your product if they're not somehow compensated for it?
(Service idea: a Q/A site where people could ask questions about their products as they're building them. Does this exist already? Some subreddit maybe?)