I had a stamp almost exactly like this uploaded back on !Heiderich-Luvur
but it got lost when I was moving all my crap over here.
So I made another one because I think that this really needs to be said.
Those who don't like slash often use this as their primary argument -- the idea that changing the sexuality of a character changes the character entirely. A person's sexuality should never be a part of their personality, just as a person's hair color, ethnicity, religion or gender shouldn't define them.
Some say that that's the opposite, and yes, it's true that some personality traits are attributed to the above things, such as blonds being stupid, Christians being bigoted, girls being sensitive, and Asians being smart.
However, these stereotypes are often the exception rather than the rule. There are dumb blondes, yes, but there are very smart ones. And very dumb brunettes. There are wonderfully open-minded Christians and very close-minded atheists. I've known girls who want nothing to do with love and boys that cry at Disney movies.
So saying that, for example, making Superman gay for Batman, is changing both of their characters entirely is, in fact, a very false statement. Gay or straight, Clark Kent would still save the day. He would still work at the Daily Planet and have a secret identity. He would still be idealist and moral, wanting nothing more than the good of the world. Bruce Wayne, no matter his sexuality, would still be darker and more mysterious. He would still be as precise and angsty as he always was. And, furthermore, whether their relationship was friendly or romantic, the two heroes would pretty much still interact in the same way. Bruce would be cynical of Clark's idealist nature and Clark would always be trying to get Bruce to be more optimistic, just as they're doing for each other now. We both know that the characters are capable of love, thanks to Rachel (in Nolan-verse) and Lois. So there would be no character change whatsoever with Bruce/Clark slash.
Of course, there will always be those who change the character's personalities within their slash, and I'm not speaking for those people. We all know that Rorschach won't be leaving roses on Dan's doorstep, and Envy will probably never cuddle with Ed. That's a different situation, and that exists in het, too.
But saying that slash isn't even possible because it changes the personality of the characters is an erroneous thought process. I wouldn't be a different person if I was straight. I would still like the same things I like now. I would just be attracted to men rather than women.
So, to put it bluntly, 'gay' is not a personality trait.