Re: Who are these people
"It betrays an obsession with feelz and a demand for ideological purity which many people find revolting."
Yes, but then I find lack of politeness pretty irritating also.
"You don't need a CoC to deal with what is illegal."
Yeah, you do. Most organisations have relatively strong policies relating to bullying and harrassment, and a mechanism with dealing with it. And they have to because if they do not they will appear complicit. Look at is this way: child abuse is illegal, but does that really mean that schools do not need to have policies for safeguarding children? Of course, this is not to say that a CoC is needed to cover all potential illegality; there is little point in saying "murdering people will be grounds for removal" because that is just silly.
In the case of Linux, "legal" is made more complex by the multiple jurisdictions that people find themselves in, so being explicit about the project may help.
"It's mostly obsessed with sex, race and gender."
These are legally protected characteristics in many jurisdictions. By definition, any policy about harrassement is going to involve these characteristics.
"Can you express thoughts regarding illegal immigration without falling foul of this?"
That's a good question. The CoC gives you a basis for making a decision on these things, but how they are applied in practice is very important. I would hope that you could express thoughts about illegal immigration even though, I suspect, I wouldn't like those thoughts. Similarly, for instance, while I think discrimination on grounds of religion is a bad thing, I would like to be able to say that most religions make little sense.
If it works badly, indeed, you might be excluded from saying such things. If it works well, then, perhaps linux (and other free software projects, including some I contribute to) will become a politer place to be. I am hoping it goes well.