Why do people think marriage is a right?

Because the American political lexicon has perverted what many of these words mean. Limited government, pro-choice, and marriage rights are all liberal ideas. Socially obstructive government is neo-conservatism. You could call the belief in small government neo-liberal. It's weird. Modern American conservatism is a combination of neo-liberalism and neo-conservatism. It's a match made in Hell that contradicts itself often.

Shouldn't conservatives want same-sex marriage? It'll boost small business revenue for florists, photographers, wedding venues, dress stores, tailors, caterers....

Because there's a difference between rich conservatives and poor conservatives. Rich conservatives know what they're doing, and advocate for the deregulation of their businesses so that they can cut corners and make more money at the expense of the environment, their workers, and their country. Poor conservatives are sheep who will follow anyone that claims to stand for "Christian" values, including these sharks, hence the apparent conflict of interest. Not to be outdone, a similar dichotomy exists for liberals, though the poor largely benefit from it in the short term. More powerful than either faction is a group that seeks to expand the power of the US government, a group that both factions serve. Whether you consider it nation building or imperialism ultimately has as much significance as your choice of soda flavor.

Conservatives don't [i]actually[/i] believe in small government.

Libertarianism FTW?

Because it's wrong to have the big bad government man tell you how to live your life, but wait you two can't get married, that goes against the sanctity of marriage, and is not what the big good God man wants. #what

One of the goals of movement conservatism, the brand of right-wing politics popularized by the Reagan administration, is to dismantle all economic policies that infringe on wealth accumulation (income and capital gains taxes, estate taxes, corporate taxes etc.) and facilitate the broad distribution of capital. Essentially, they espouse the rollback of New Deal and Great Society policies to the pre-1930 socio-economic model. The movement entrenches with Fundamentalists and other values issues (WASP, pro-life, war on drugs, no to gay marriage) to gain votes they would otherwise not have, the core of their ideological movement is contrary to most American's best interest. Otherwise, there would be little need to "have alliances with religious fundamentalists, no need to exploit morality or lifestyle issues."

Shit happens. Join the moderate party!

Cause hypocrisy.