Gay marriage is legal throughout the United States of America! The United States Supreme Court decided in the Obergefell v. Hodges case that banning gay marriage violates the Constitution of the United States. Before this decision gay marriage was illegal in many conservative states but the majority of states allowed it. 
Banning of gay marriage was a violation of the US Constitution under the 1st amendment. This is because seemingly the only argument against gay marriage is on religious grounds, and the Constitution prohibits the establishment of religion in the law. Gay marriage bans also violated the 9th amendment (individual rights) and 14th amendment (equality under law). Social conservatives who are homophobic tried to make this illegal, mainly because this was a wedge issue that they could use to get ignorant social conservatives to go vote Republican. At least it was a wedge issue but American voters overall became more accepting of gay marriage. Anyway they can't use that issue any more.
The United Kingdom
The law is different in different parts of the United Kingdom. Same-sex marriage is legal from March 2014 in the England and Wales, Scotland is debating the issue and will probably legalise it but Northern Ireland isn't planning to allow it. 
What Conservapedia (who claim to pride themselves in teaching economics) fails to understand is that gay marriage could be a massive economic solution. Millions of gay couples spending thousands of dollars on their weddings would pump BILLIONS into the economy, as well as attract tallented gay people to places where their human rights are recognised.
Roman Catholics and Protestant Fundamentalists oppose gay marriage but Liberal Christians are more supportive. Of course there are many religious types in between the two extremes. Churches that are LGBT-affirming religious groups will marry gay people when this is legal. Sympathetic churches will do a service of blessing for a gay partnership where gay marriage isn't legal.
Why so many heterosexuals support gay marriage
- No darling! We shouldn't do that till we're married.
- No darling! Even when we're married we shouldn't do it that way.
- No darling! Even when we're married you shouldn't put that thing onto your willie.
And after they've married straight men are tired of their religious wives telling them what (God or their religious leader) does and doesn't want them to do in bed. People sometimes would rather change from the missionary position, many Conservative Christians don't like that.
- Nice Christian girls don't have their skirts too short or their pants too tight.
- Nice Christian girls don't have their necklines too low or their sleeves too short.
- Nice Christian girls don't wear bikinis.
- Nice Christian girls don't go to dance halls where they could meet the wrong types of men.
And so it goes on.
- Very many Human beings of both sexes and many different sexual orientations are tired of religious people telling us what we should and shouldn't do with our own bodies or with our consenting adult partners.
- Very many Human beings of both sexes and with very many different sexual interests sympathise with gay people because we've also had trouble over religious prudes trying to regulate our sex lives.
- We understand how gay people feel when churches try to stop them getting married. After all we also have problems or had problems in the past with churches trying to stop us doing the things we personally like to do.
- Same-sex marriage legislation in the United States by state
- Gay marriage: Eight things for better, for worse Gay marriage is proposed in the UK
- Gay Marriage
- "Defenders of Marriage" Video ridiculing conservatives who oppose same sex marriage by Roy Zimmerman