Which is the more morally detestable action. To discriminate against people due to the color of their skin, or to discriminate against people due to their religious beliefs? On both accounts one discriminates against an involuntary characteristic, race being innate, and religious views being a matter of conviction. In the question, I assume that one cannot choose ones conviction, one cannot be forced to believe in God, not truly. Thus, being convinced of the truth of a certain religion is involuntary. Therein lies my question, if we accept the moral detestability of racism, should we also accept a moral detestability of religious prosecution? And if so, wouldn't morality dictate the refrain from verbal offenses against religious people, on par with those against races?

There are at least two issues here. One is whether race and religious belief are involuntary in the same way. Another is whether it's ever okay to discriminate on the basis of a person's beliefs—religious or otherwise.

On the first issue I'm going to simplify by mostly setting aside some important questions about whether there is such a thing as race in any deep sense, and just what race amounts to insofar as there is such a thing. The important point is that in typical cases, there is for most any practical purpose nothing people can do about their race; racial identity is strongly involuntary. That's not so clearly true of matters of conviction. There's nothing at all unusual about people changing their convictions, including their religious convictions. Non-believers become believers; believers become non-believers. This doesn't tell us whether such changes are voluntary, but it's an important difference.

Are such changes belief voluntary? That's too simple a way to frame the issue. It's often said that we can't simply decide what we're going to believe. I could no more decide to believe that there's an elephant asleep on the bed behind me than I could pick up that bed (even without an elephant on it) and crush it into a fist-sized ball with my bare hands. But I can decide to reconsider at least some beliefs. I can decide to seek out reasons and evidence on both sides. I can resist the temptation to ignore facts that count against my predilections. That's not the same as simply deciding to change my mind, though if enough evidence accumulates on one side, I can make the effort to focus on that evidence. If it makes me uncomfortable, there are techniques that will help me sit with that discomfort and not simply give in to it. In short: belief isn't simply voluntary, but in exactly the sorts of cases you have in mind, it isn't simply involuntary either.

We can go further: on important matters—especially if they affect other people— we have a responsibility to pay attention to the evidence and to try to be guided by it. Failure to do that can amount to a legal offense (negligence), but it can also be a moral failing. If someone is unwilling or unable to take what we might call epistemic responsibility, this can be a legitimate reason for at least some kinds of discrimination. It might be a reason not to hire the person to watch your kids, or a reason not to appoint them to a position of power, or a reason to vote against them in an election.

That's all general. In the case of religious belief or lack thereof, the details will matter, but that's true in general. Some people might be best described as brainwashed, but some might just be stubborn. That will make a difference when we consider how much blame (or credit) they get for their beliefs.

Responsibility for one's beliefs is a subtle matter, but we don't need to sort it out to answer your last question. The mere fact that someone disagrees with you about an abstruse and possibly undecidable matter is seldom likely to add up to a reason for discrimination. In particular, persecuting people or even insulting them for their beliefs or lack of beliefs is almost never going to be acceptable. Nonetheless, this isn't because one's religious commitments are involuntary in the way that one's race is. In important ways, the two cases are quite different. What beliefs we end up with is not simply out of our control, even if it's not straightforwardly voluntary. Those differences suggest that bad as it may be to persecute people for their beliefs, it's even worse to persecute them for their race.

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