"If we cannot have moral feelings against homosexuality, can we have it against murder?"Not how I would have asked the question, but he is getting at something very interesting. Some of the reaction, however, has been frustrating to me. Some have been offended, because how could a prominent public figure compare homosexuality to murder?
Which is fine, I suppose. I think some people like to get angry at people who disagree with them about important topics, and this is certainly an important topic. Perhaps you could even make a pragmatic argument that angry reactions are more likely to stigmatize heterosexist viewpoints, and thus progress us more quickly towards a more accepting society.
For me, though, I think it's likely more helpful, and certainly more interesting, to deal with the substance of Scalia's claim. As he subsequently pointed out, he was engaging in a form of argument called a Reduction to the Absurd. Basically, you assume that a given premise is true, and then show that it has absurd implications, and thus must be false. It's a great form of argument!
The way Scalia has phrased the argument is not the best. It's not clear what place "moral feelings" ought to have in any kind of decision procedure, legal or otherwise, so it's not a helpful concept to employ. Nevertheless, I think we can show the Justice the respect of trying to understand his argument in the best possible light. That way, when we successfully criticize it, we can be more assured of our own position, and more likely to convince others.
I think Scalia is best understood as making an argument as follows. All moral arguments rest on some kind of intuitive judgment of right and wrong. Most people judge murder to be wrong, and some judge homosexuality to be wrong. But both of these judgments are based on similar kinds intuitive judgment, and if you disregard the kind of intuition that some have that homosexuality is wrong as illegitimate, you have no reason to rely on the more widespread intuition that murder is wrong.
This argument could be responded to by saying that since the intuition against murder is nearly universal, it's more legitimate than the intuition against homosexuality. Perhaps. But as a Justice, the interesting question would be, what kinds of judgments are illegitimate even if the majority of citizens hold them? In the case of legal discrimination against homosexuals, for example, we might want to say that the minority of homosexuals ought to be protected against the majority's bigotry. But then shouldn't the minority of murderers be protected from legal sanction against the majority?
So what's wrong with Scalia's argument, as I have re-cast it? Well, for one, intuitions are not the sole basis of ethical judgment. One of the things we have intuitions about, after all, are moral principles, and applications of these principles can lead to conflict with our other intuitions. So we have to do is work through various kinds of cases, and various renditions of principles, to arrive on more considered moral judgments. It's a very complex form of reasoning, but we do it all the time!
One of the great foundational principles of liberal democracy is J. S. Mill's harm principle. That is, that one's freedom extends only so far as one is not harming someone else, and at this point the state has a right to intervene. Now, there is some controversy around this principle, and much vagueness in what constitutes "harm." But it certainly gives us a clear distinction in the reasons we have to object to murder and the reasons some object to homosexuality.
One thing that is less clear, however, is how to distinguish between reasons for legal discrimination towards homosexuality, and reasons for motorcycle helmet laws. Some might see this problem and conclude that motorcycle helmet laws (and the like) are as illegitimate as discrimination against homosexuals. There are some good alternatives, though, such as arguing that the benefits to wearing a motorcycle helmet are so overwhelming, and the costs of wearing it (and enforcement of the law) are some trivial that the public does have an overriding interest in accepting such laws. This kind of defense is tricky, and requires a lot of spelling out to make persuasive, but I think some version of it is plausible. Regardless of this particular issue, we should definitely see ourselves as having a heavy burden for any legal restriction of liberty that is not in accordance with the harm principle.
But, once again, I think it's much better to have this kind of discussion about the foundations of moral and legal judgments than to just sneer at cooky old Scalia who was right to ask the question. He's wrong in his implied answer, but he's wrong for interesting reasons.