I think this is a valid comparison. And I'd also like to add that unlike black folks, no one in America was ever a slave based on their sexuality. They were never not counted as citizens. It's always been illegal to kill them. This cannot be said for black folks. Stop and think about the horror of that for a second. At one point in time, right here in the United States of America - the land of the free, it was perfectly legal to kill black people. That ought to make your stomach turn. Now compare that to what homosexuals are upset about. Does it not seem rather petty in comparison? This is a big reason why I think comparing homosexuality to civil rights is a huge slap in the face to everyone who suffered through slavery. It trivializes the truly apalling subhuman treatment that some people really have gone through as a result of not being legally recognized as equal. This isn't even apples and oranges. It's apples and motor oil.
It is impossible to be both selfless and pro-abortion. The latter negates the former. It doesn't matter how much money you want to redistribute to the poor. Killing your own child for convenience is the ultimate act of selfishness.
An oppressive, totalitarian, anti-gun, anti-free speech, pro-life communist still understands the value of human life better than a "pro-choice" libertarian.