I don't think is too complicated. It is perhaps just a matter of personality and empathy. When a man sees two women kissing, he can empathize both, it's too many womenly. And perhaps there is a thorn about satisfying your partner, so when TWO girls are enjoying sex rather then one, this unsees wound mends, because there is double the pleasure hanging around the scene. Besides, all he can see is double the boobs, double the asses, double the.. well. everything doubled.
But when it comes to two men kissing... Now it's empathy again, but you are into something repulsive if you are strict about such things. Because the is doubled. For some individuals, all these can be reversed I guess. Like bisexuals which can enjoy both.
And when it's not just kissing, but having it to the end, there is always some unsatisfied part when a man - at least me- watch two lesbians. Some part of the ritual is broken, now satisfaction is doubled the but the male part is missing, the part where woman "takes in" - not the pyshical part - but all the satisfaction part - of the man. Yet the other parts are so exciting you can give up the final part.
Advanced Wordsmith
Wat do u think i will love my love.....................it will really be hot mean the hottest ..... 
