Because it sure as hell acts like one.
It's basically a form of magical thinking: the assumption that someone's ethnic or genetic heritage automatically implies certain traits. It's not logical, and it causes people to suffer in their daily functioning, although it mainly forces that suffering onto people who do not have the disease.
Just like a mental illness.
Also, people who suffer from it often don't know they suffer from it.
Just like a mental illness.
There's also great stigma against admitting you suffer from it.
Just like a mental illness.
There seems to be a movement towards de-stigmatizing mental illness so that people who suffer from it don't feel a barrier to getting help. Wouldn't classifying racism as a mental illness demand the de-stigmatization of racism?
Imagine this scenario: You see someone telling a racist joke, and instead of laughing (which is an appropriate reaction to anything worthy of ridicule) you just get morose and say "Oh, I didn't know you were suffering from racism. I hear there's a medication for that. We would probably all be happier if you were on drugs"
And let's say, just for giggles, you could get approved for medical marijuana if you were diagnosed as a racist by a doctor. I mean, seems plausible. Stoned hippies are rarely racist.
Of course you would need a high level of involuntary secret medical surveillance over everyone in the united states to make this plan work, but frankly we already have that to catch people with drug dependence, PTSD, anxiety, anger management issues, and other mental health issues that can lead to criminally disruptive behavior. The only thing the medical industry lacks is funding. Please note I didn't mention consent, because many mental illnesses are treated involuntarily, especially drug addiction which is the main model for this sort of intervention.
I mean, how else are we going to stamp out racism? All other forms of ignorance are fought with compulsory education, why should this one be any different?
This is a song about death. It's on mandolin.
Hate is the first step to all solutions.
You will not end bigotry until you learn to hate it.