Unicorns seem to be a metaphor for male homosexuality.
Example:
http://www.echonyc.com/~stone/Ethan/Mostly/EthanNewAge.html
But why?
And does this have anything to do with the unicorn dream sequence in Blade Runner?
http://www.youtube.com/watch?v=xhDDybv8_Ro
Updated by RedOctober