Actually they were used by men back then for the same reasons women wear them now, to look fabulous. They started being used by Persian men to ride horses better and fight better on horseback. This started a craze among the european social elite and spread to their women and then the commoners so the elite made the heels longer to be more impractical as a show of wealth. Then the craze was for men to wear practical less flashy clothes, but not women, and a more pronounced difference in the sexes was also forming. Thus heels became to be seen as feminine and foolish for men to wear.
I'm probably oversimplifying things a bit so don't take my entire word for it.

>"foolish for men to wear"
i beg to differ: