Look at what happened to abortion.

Most countries that have gay marriage are Catholic like Mexico, Argentina, Brazil, Spain, France. Canth say the same about Protestant, Muslim, or even Atheist countries like China and Russia.

In 2008 even Obama was against gay marriage

Mexico has gay marriage written into law by its 32 state legislatures. USA has gay marriage because of a Supreme Court decision that could be over turned any session. So in a way Mexico gay marriage is like a constitutional amendment so it's way more robust than what the US has

No. Most countries have just the capital and cities