I’ve seen people asking the question or making the complaint several times: Why don’t people whose religious or other similar convictions are against something, like same-sex marriage, just keep it to themselves? Why do they insist on trying to make others conform to their beliefs as well?
The answer, as far as I can see, is depressingly simple.
What they actually think is not that it’s against their religion (or whatever). They think it’s wrong. And one does not allow morally wrong things to be done just because someone else thinks it’s okay.
In a society with a variety of cultures (and I don’t just mean associated with people from different countries, every religious group has its own), everyone has to get used to dealing with people who don’t take the same things for granted as they do. So, a person’s version of their religion might forbid X, and among people of the same group, it’s taken for granted you shouldn’t do X. But outside that group, the person can’t just act shocked at the suggestion of doing X and expect to be understood. Hence we get the classic explanation: “It’s against my religion.” This kind of talk in different varieties is already quite normal in modern societies.
But that doesn’t automatically mean people with different values think of them as just peculiarities of their own traditions that are arbitrary. Sure, some will notice they’re just traditions and not inherently important the way people used to assume. And some traditions have the nature of really only applying to one’s own group; Judaism with its rules of conduct seems to usually exemplify this, more or less. But in some cases, people still just think some things are wrong, and if it’s their religion saying so, that just means it’s stated on the highest possible authority.
And in such cases, though the people may or may not explain their views in the weaker terms of “my religious convictions” or whatever, they’ll see such things as objective moral requirements or prohibitions, not just their quaint little tradition. The rest of the world won’t agree, because they don’t share the same beliefs about the authority of that tradition and suchlike and really can’t see why they’re supposed to care. But that doesn’t change the fact of how the group itself ultimately sees the matter.
So really, though what they do is wrong, people like for example Christian conservatives opposing same-sex marriage are not wrong in opposing what they see as being wrong. It’s right to oppose that which is morally wrong, and someone opposing an actual wrong thing would have my support. They are wrong in seeing that thing as morally wrong in the first place; they’re wrong in thinking their tradition is reliable and has such moral authority, wrong in thinking something can be morally wrong that harms no concerned party, wrong in their beliefs about what homosexuality is. But they do not think what they’re imposing on others is just their personal religious view. (In that too, of course, they are wrong.) So they are not thinking it’s okay to force one’s personal religious view on others. The answer to why they try to do it is that they think they’re doing something else.