Logically, I don't see where "Chinaman" is any worse than "Frenchman", "Dutchman" or "Englishman".
True, Chinese people are not actually made of porcelain, but then again, porcelain is a pretty high status substance.
The logical equivalent of "nigger" would be "coolie", I suppose.
Most White folks who use the word "Chinaman" are not aware that anyone takes offense from it. It seems to me that to take offense, a person should have to be aware that offense was intended.
I think Michael Richards was way over gthe line, but I hardly think it merits any sort of lawsuit. It is not nice to offend people based on their ethnicity, but it's not illegal. I don't think it should be either. Threatening people with physical harm is something else, though.