I, for one, think there’s nothing wrong with such quid pro quo. You should be able to buy politicians all you want, just like you buy everything else. Governments shouldn’t be granting special status to gay couples, is all. Whether someone votes their conscience to allow it or is bought off, what’s the difference? Oh, you think you can control it and keep it good and pure and stop governments from being manipulated for private ends thereby? Fat chance. Has it grown more or less corrupt and extensive since do-gooders went after the root of all evil? Yeah.
Time was, when politicians were bought, they stayed bought.
And a politician that can be bought, will be. Especially when they have all that power (supposedly to do good, as you pointed out.)
Government limited to its proper functions is a lot less attractive target for corruption.