alt Hacker NewsFor one, being childless is a choice (mostly, especially since adoption is a possibility). It's indeed OK to have different opinions for what how laws apply differently to people based on their choices. Being gay is not a choice, it is rather similar to race/ethnic background, and it's generally not OK to have laws that treat people differently based on something like that. I'm sure there are more nuances to add, but it seems to me that makes it quite a different situation.
I don't think everyone agrees that being gay is not a choice. There are no outward physical indicators of a person's sexual orientation. It's entirely behavorial and therefore plausibly under the conscious control of the person. Now, I would agree that a person doesn't choose which gender he is attracted to, but it not something than anyone else can see and immediately understand as an inborn characteristic.
Clearly being black, or hispanic, or asian, or white are physical characteristics. Far fewer people would argue that there is any element of choice in that.