My main argument for 1 person startups would be you need someone to call you on your BS. It's incredibly easy to pretend a problem isn't a problem or a solution is a good one when it really isn't. It depends on the area of business, of course, but in my particular field, rolling solo would be very dangerous.
You can have mentors and friends to help with BS calling if you are willing to listen. But ultimately they will not always be right, so you risk not following a valid idea far enough.
