1) Mental Retardation Is Objectively Negative.
Well, to put it bluntly, so is being a woman, being queer, or being a racial minority. All of these groups will be worse off than a straight white man for various measurable factors, so that doesn't give any reason why it's acceptable for one but not the other.
2) Mental Retardation Is Objectively Worse.
There are a number of cases where someone that is mentally retarded is objectively better off than someone from another, "less severe" minority. For example, every victim of a gaybashing, all the women gunned down by Eric Gault, the victims of lynchings... So that's also another no-go, because it's not so simple.
Are you intentionally missing the point? Or are you just dense? Being female, gay or a racial minority have downsides due to discrimination. A female is not objectively worse off just by virtue of being female, but because of social prejudices. Mental retardation is objectively negative because it's having something wrong with your brain.
By calling someone retarded, you are implying that they are less capable intellectually. People with mental disabilities are functionally, objectively in a position that is undesirable, not merely because of social ramifications, but because of their reduced ability to function.
It's a word, that yes, has been used as a medical term, but ultimately, when someone uses the word "retarded", they are using it interchangeably with the word "idiot", or "moron", both of which share the same roots, as terms used by psychologists to describe the mentally handicapped.
Using the word "retard" is insensitive to people who do legitimately suffer from mental disabilities, and I can understand that, but almost every insult that exists was or still is a word that has discriminatory roots, and at least when you're calling someone a retard, your insult has an objective, negative association. No one wants it implied that they're brain damaged. There are few insults I find offensive, because I don't find being female, feminine, homosexual, etc., to be inherently bad. Calling me a retard offends me, because it's an explicit accusation of having a mental disability. An insult to my intelligence.
Discriminatory or not, it is an effective insult. It means what it means. What would you prefer, people using nonsense words as insults?
Ford Prefect wrote:
Around these parts people are mocked because they are stupid. Saying that someone is retarded because they are stupid makes more sense than for example pointing out their sexuality, their sexuality has nothhing to do with their inteligence.
This fundamentally misses the point: that by using 'retard' as an insult you are perpetuating a kind of dehumanisation. It's a type of bigotry, which is not substantially different from slurs based on race, gender or sexual preference. Or even using obesity as a source of slurs.
All intentional insults are dehumanisation. That's kind of the point of them. They're a word you use to put another down. To make them feel less of themselves, or to express that you think less of them.
If you use the word ugly as an insult, you're being bigoted against those who aren't physically attractive. And for that matter, calling someone stupid is implying that a lack of intelligence is a bad thing, and that's clearly bigotry! Gosh. ABLEISM!
I don't like people using the word retard as an insult. I try not to do it, because I know people who are mentally handicapped, and consider them friends. I have an aunt with Down's Syndrome. But unless you're going to start decrying insults in general, to call it bigotry on par with racism and sexism is missing the god damn point that having mental disabilities is genuinely a bad thing. It doesn't make you a bad person, it doesn't make you less of a person, but it is a bad thing. It is a thing you don't want. And to have it implied that you're mentally disabled when you're not is offensive. That's why it's used as an insult, and that's why, while racist, homophobic and sexist insults may fall out of usage as those groups become less dehumanised by society, words that insult intelligence won't go away, because regardless of how discriminatory they are, they have a meaning the will always