There are certain kinds of moral belief that we view in a pluralistic manner, and others that we take to be absolute. For an example of the former, suppose that I'm a vegetarian who believes that eating meat is immoral. Most people would say that it's inappropriate for me to harangue meat eaters, since they are just as entitled to their beliefs about diet as I am to mine. By contrast, we don't reason this way about things like murder. I am not obligated to respect the beliefs of someone who thinks murder is permissible--on the contrary, I may be morally remiss if I don't try to stop or correct him. What explains the difference between these two kinds of moral belief?

It's an interesting question. Some thoughts.

Suppose Rufus believes that murder is morally acceptable. If I know of a murder he's trying to commit, then most of us agree that I'm not just allowed but even obliged to do various things to prevent it. (Telling the police would be the most obvious.) But if I have no reason to think that Rufus is planning to kill anyone, then while it's perfectly okay for me to try to argue him out of his view, most of us don't think it's okay to harass and harangue him about this admittedly despicable view. One reason for this is a matter of keeping civil peace; more on that below.

Of course, there may be gradations here. Suppose it's not just that Rufus thinks it's okay to commit murder; suppose he makes a career of trying to convince other people. We'd still think there are limits to how far we can go in protesting, objecting and so on, but the limits would be fewer than they'd be if he were just some random weirdo who wasn't likely to act on his views and also wasn't likely to persuade anyone else. I don't have a theory of what the boundaries would be, except to say that they'd depend on the details.

In any case, you're right that we make distinctions. If Rufus is about to go out and commit murder, it's more than okay for me to try to stop him. If he's preaching that murder is acceptable and I shout him down, I'm probably pardonable. If he's about to go out for a sirloin, then short of trying to talk him out of it, there's not much that it's okay for me to do. And if he's merely arguing that it's okay to eat meat, then conversation about it is pretty much the limit of what's appropriate. What are the differences?

One difference is specific to the example: many of the reasons for thinking it's wrong to kill animals for food have parallels when it comes to committing murder. But there are other reasons for not committing murder that don't have parallels when it comes to killing animals. The point is that it's hard to imagine a coherent view that forbids meat eating but permits murder. We might put it by saying it's clearer that murder is wrong than that eating meat is. We also might be willing to add that even if eating meat is wrong, it's arguably less wrong than murder. In any case, when one sort of judgment seems less clear than another, we're less inclined to impose our own conclusions in the former than the latter.

In other cases, it's not clear that one side has the intellectual upper hand. It's quite possible to hold a moral view and to recognize that someone can disagree without ceasing to be reasonable, let alone becoming a moral monster. In cases like this, a proper modesty about one's own wisdom calls for respecting the opposition. Going a step further, if you hold a moral view that's widely doubted, you may be in the right, and eventually it may even become clear to most people that you're in the right. But it's also possible that you're missing something that other people see and if there are reasonable people among your opponents, you've got a reason to take this possibility seriously. In cases like this, trying to persuade others is fine. Haranguing and harassing is not so fine and suggests that you may have a deficient sense of your own fallibility. And of course, imposing your view by force is out of bounds.

This is a sketch of a morally imperfect system, of course; it's sometimes gotten things badly wrong. But quite apart from having a sense of modesty about one's own wisdom, there's the question of what the world would be like if we didn't restrain ourselves in something like this way. There, we tend to suspect, lies chaos. And chaos doesn't seem like a likely route to moral improvement.

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