Hollywood casting

kris
Do you think Hollywood should make an effort to cast according to sexual orientation? For instance, gay men should only be played by gay men. And straight by straight. I would be afraid that it would greatly reduce the number of gay actors getting roles since there aren't many gay characters on film. And I have a hard time seeing how that wouldn't be discrimination. But I've also heard people compare it to someone's race and how you wouldn't hire a white woman to play a black woman and vice versa. But I'm curious what others think. 
As I'm not gay, forgive any accidental ignorance. It was a curious argument I came across the other day.