Bald men are people losing hair cause of evolution. In a way, bald people are more "evolved" than people with hair. As regarding to what women find sexy and not, you can do a lot of things about baldness today. If your perception about baldness is that it looks creepy, plant some hair in the areas where you lack them and have hair. If you think it's OK, shave it completely. I think a patchy had might look not nice, that's all.
Personally, I think it's a minor factor for most women anyways.
The full evolutionary story, according to physical anthropologists, is that female humans (here "human" pertains to those of the Homo genus) having a less hairy buttock area presented a stronger signal of the standard genitalia bloom that fertile female anthropoids show in heat - and being that the males were getting more intelligent, they began to hone on this signal more, and thus women with bare buttocks were sought out. The genes that control a "bald ass" also control to some extent hairless in general, which is why humans are so less hairy than our fellow anthropoids. The reason that the head continued to have hair is of course because of the heat insulation and protection from the sun (i.e, to cut out skin cancer). Long hair in a maiden was a show of fertility, just like any sign of youth & strength, so women who were bald were considered very unattractive, and thus women today are by & large not bald, at least during their fertile years. One would imagine that the baldness of a woman's face was viewed upon in a similar way to the buttocks, resulting in women being beardless. Also, a man's beard began to be viewed as sign of physical health in the same way that a woman's hair length was.
It is a well-known fact that men typically take after their mother's brothers in terms of baldness (although not always, as except for a yarmulke bald spot, I have a strong amount of headtop hair, and my mother's brothers looked like Kojak), which would seem to indicate that some that attractiveness in a woman having a bald buttock rubbed off on the genes of her male relatives. Perhaps the unattractiveness of baldness was evolutionary masked by the institution of marriage, and today's women's aversion to bald men in general (except for the ones that are more attracted to brutes, which baldness tends to be seen as being correlated with) is just part of the hypergamy that has resulted from society's loss of control over female sexuality.
I find it rather instructive that the last really bald non-accidental USA President was Eisenhower, and there have only been 4 others, at least before the current combover era.
http://www.huffingtonpost.com/2012/..._2083612.html?slideshow=true#gallery/261551/0