I think guys often perceive male-male experimentation as worse because some feel their masculinity is threatened. The whole macho male stereotype instills into guys that they should be strong and not show much affection for even their closest friends. Whereas females are encouraged to be affectionate towards all people regardless of gender. Basically I am trying to say that the attraction (however strong or weak) for another male goes against many social perceptions of how guys should be/act and that this could be a reason why some see it as "worse" than female-female experimentation.
~ The journey of a thousand miles begins with a single step ~
* Nothing in the world has ever been accomplished without passion *