I don't mind working with someone who has incompatible views with me, but I'd be quite unhappy working with someone who was actively working on undermining my rights.

Why is the reaction seen as irrational or immature but not the action that triggered it?

It's one thing to believe as you do, it's quite another to push for legislation that would (in your example) deny childless couples societal advantages, whatever that actually means.

If you're not in favor of a-or-b arguments the answer is to allow a and b, eh?

You could argue that there are laws that only apply to married couples, and that THAT brings meaning to marriage. But:

Firstly, generally speaking, even the most important features of a marriage are not protected by law, most notably: fidelity. So the law is disjoint from what's traditionally considered to be obligations within marriage. That leaves the legal definition at the whims of contemporary polititians. Therefore, law cannot assign the word "marriage" any consistent meaning throughout time.

Secondly, to my limited knowledge, the line between a married couple and two people living together is increasingly getting blurred by laws that apply marriage legal obligations even to non-married couples if they have lived together for long enough. It suggests that law-makers do not consider a ceremony and a "marriage" announcement to be what should really activate these laws, but rather other factors. Although, they seem to acknowledge that an announcement of a marriage implies the factors needed to activate these laws. If that makes sense...

So marriage is inherently a religious institution that in a religious context comes with rules, obligations and rights. Hence why people who take religion seriously will find it offensive that somebody that completely disregards these rules calls themselves married.

So when a person wishes to deny this important institution to a minority, they are creating an out-group and discriminating against them.

By that logic, we can put those discriminators themselves in an out-group and discriminate against them. We can deny them institutions such as directorships. Fair's fair.

It's more than fair - despite what conversion camps want to sell, being queer is an intransigent characteristic. Being a bully is just a choice. Discriminating against bullies is as morally just as discriminating against the incompetent.

Obviously it's fine to campaign against marriage.

Pretty much all of the legal benefits of marriage are contractual, not financial, and come at no cost to the public.

Things like spousal medical rights, a joint estate, etc don't come at the expense of anybody else.

That's right. To get a bit philosophical, it's interesting to see some people's justifications about how they are right to be intolerant in the ways they want to be, while still believing that they are free-thinking and tolerant. A lot of convoluted arguments are really about keeping one's self-image intact, justifying beliefs that are contradictory but which the person really wants to believe. I think that is a trap that is more dangerous for intelligent people.

For what it's worth, I support and supported gay marriage at the time, but don't think people should be forced out of their job for believing otherwise. Thoughts and words you disagree with should be met with alternative thoughts and words.