"If you’re unable to convince friends to start a business with you, PG says it’s a vote of no confidence. But, what if you’re like me and you don’t have a lot of entrepreneurial friends? Or, maybe you do, but they don’t want to work on your ideas? It doesn’t really matter what your friends think of your ideas or you in regards to starting a business–the votes that count come in the form of paying customers. Since it’s cheap and easy to spot faults in unproven business ideas, early votes of no confidence, even from well-meaning friends and family are standard fare. Expect and take them with a grain of salt. Some of the best companies today sounded pretty dumb on paper yesterday."
This is probably the clearest refutation of Graham's single founder section I've seen.
I'd expound a bit on one of the later points:
If what you're doing is somewhat domain-specific, only the opinions of people in your target area and market matter. You might know a lot of people, but if they're not in your target area and market they might not get it. If you're getting negative feedback from them, it might be irrelevant. The only negative feedback you should listen to is from people who really get your target area.