I guess I only NEED one (and in my current situation I haven't actually NEEDED a handgun at all for many years). But one handgun I'm proficient with, in a serious caliber, to make man or beast take notice, is all I really need.
That said, shooting is a hobby and a sport of mine so for me to feel happy and satisfied I actually NEED more than one for the different shooting I do.
P.S. Do NOT forget about a black powder gun. We must all touch bases with our roots now and again!