I feel that the perpetuation that men with long hair is a bad thing is a social norm that needs to die out. I once tested a theory walking though my town center, looking at all the men and women I pass, at how many women had long hair compared to men. I came to a rough conclusion that around 90% of women I saw had long hair, or long hair tied up, of differing lengths, while men, only like 3-4% had long hair.
Its a social construct that men with long hair is bad while women with long hair is acceptable.
I think if the guy is sexy already, then long hair adds a level of ruggedness that short hair wouldn't achieve.