Nerds_feather
Purveyor of Nerdliness
Speaking as a (much-faded) redhead....
While I wouldn't say that having (naturally) red hair in the UK has, or has had, the same disadvantages** as having, say, dark skin, it is something that's the result of one's DNA and so cannot be helped. And yet at the same time as attacks*** on red-haired people were being seen as nothing to worry about (by people whose hair wasn't red, naturally), the previous government was trying to say that believers should be protected in the same way as ethnic minorities. (Of course, people should never be attacked for what they believe, any more than they should for being who they are, but ideas should never be protected from criticism.)
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I think the major difference I see between, say, prejudice against red-headed and prejudice against, say, blacks, is that red-headedness often doesn't pass from one generation to another (even if two red-heads have children together). So it never quite has the same "groupist" dynamic. But otherwise it sounds like it can get pretty awful over there.
As far as religious-based prejudice goes, well, it can be nearly the same as racism or ethnocentrism--where one ascribes an "essence" to all members of a faith or sect and then uses the assumption of that "essence" as a rationale for treating individuals from that faith or sect poorly. Or it can be quite different. Unfortunately, there are some people who use "I'm just criticizing the idea" as cover for the blanket prejudice thing. This is why I think the smell test is often necessary--it's a bit more complicated in this case than with straight-up racism, but I think it's often quite clear.
That said, of course I believe in the legal right of people to say whatever they want--including hateful speech (short of that which explicitly incites violence). I find it abhorrent, but I see a degree of abhorrent opinion-making as a necessary evil in an open society. (In private settings, there's no such guarantee of protection.)