Some of the most irrational arguments I've run across in the debate on marriage equality are 1) the claim that equality supporters are being intolerant, and 2) what is happening is just a "difference of opinion."
What is the "difference of opinion" being discussed? Some think gay people ought to have the same rights as everyone else; others think they should not have the same rights.
What is the second group claiming? They assert a right to use legal coercion to impose burdens on a group in a way known to harm them. These are people who, in spite of any arguments they hide behind, are asserting a right to inflict harm on others. That is more than a difference of opinion!
A man sneaks into your home and steals your television. He asserts a right to have your TV while you assert the same right. That is not just a difference of opinion. White racists in the South asserted the right to treat blacks as second-class citizens -- and would have treated them worse given half a chance. Black Southerners disagreed of course, but it was more than a difference of opinion.
When Rosa Parks refused to give her seat on the bus to a white person, it wasn't just a difference of opinion.
When people use legal means to harm others, it is not just an opinion -- it is an action. It is an action morally indistinguishable from a violent act meant to achieve the same goal.
Proposition 8, in California, was not just an opinion. It was a legal action meant to strip gay couples of their right to marry. In doing so, it put gay couples at a legal disadvantage, hurting them and their children in numerous ways.
One thing conservatives like to harp about, and rightfully so, is how regulatory costs can disadvantage one group to the benefit of others. For instance, Big Business has historically loved regulations -- lots of them. The greater the regulatory costs, the harder it is for smaller competitors to survive. It gives advantages to those who can afford the costs. For instance, Amazon is pushing legislation to require all on-line business to pay sales taxes in all 50 states. That would not hurt Amazon, but would harm smaller book venders -- precisely what Amazon wants.
Now imagine regulatory costs being imposed on one group only, but not others. That is what marriage laws do. A gay couple, in a state where marriage equality is illegal, can only achieve a shadow of the rights they ought to have through the use of private contracts. The contracts won't give them the same rights, and can be challenged in ways marriage can't. In addition, they can cost thousands. A straight couple goes to city hall, pays maybe $80 and walks away with all the same legal protections, plus some. The gay couple will also pay more in many other ways.
These are real harms being imposed. Your opinion won't harm people. It takes action, but fighting to deny other people rights is not opinion. It is action.
The second issue is the claim that gays are intolerant because they don't "tolerate intolerance."
This claim assumes a moral equivalency between all forms of intolerance. The Jew who doesn't tolerate Nazis would then be as immoral as the Nazi who doesn't tolerate Jews.
The idea that all intolerance is wrong is also the idea that there is no moral content whatsoever to all possible forms of intolerance.
Consider the equivalent of violence. Is violence wrong? The only rational answer, as I see it, is that it depends on context. A man beating his wife is a wrongful use of violence, intervening violently to stop him is not. Both acts are violent but only one is immoral. There are many kinds of intolerance, not all of which are immoral.
When you consider how conservatives whined for years about "liberals" refusing to take moral stands, it is amusing to watch them shriek in horror when a moral stand is being taken.
It simply is immoral to tolerate all forms of intolerance.