(Unfortunately, many people on learning an exciting new definition of a word forget it has a more general meaning; confusion and stupid internet arguments ensue.)
I don't know what this means. But please elaborate what's wrong with that statement. Please understand that a word's definition is not necessarily it's meaning.
The group in power can be black, as, for example, more or less is the case in the current South Africa, and may be the case in some subcultures (rappers? Basketball players? Some prisons?)
For example, if an organized group of American Asians began touting their superiority over other races and advocated and lobbied for more Asians in positions of power because they're superior, wouldn't you still consider their actions to be immoral?
People can use whichever definition they like, but they need to be open about it, and they need to realize by using another definition they're not also redefining or constraining the connotation -- that's begging the question.
So, black people cannot be sociologically-racist-therefore-immoral against white people, but they can be common-usage-racist-therefore-immoral against white people.
(I should also note that labeling something with a word that connotes a negative or positive affect isn't much of an argument for the applicability of that connotation to that something. It's a heuristic more than it is an argument.)
Also, your definition of what racism connotes is severely lacking as well. Simplifying racism to "something that connotes immorality" is a gross oversimplification.
And not only that, but words have denotations and connotations. "Ugly", in common usage, denotes and points to a set of subjective physical characteristics. "Ugly" also connotes and points to a negative affect that isn't explicit in its denotation.
I'm not simply saying that racism is "something that connotes immorality", but that is what we're connotating when we use that word in its various denotations (although, it's not necessarily the case). Racism's denotation can be literally anything. I can say, for example, that it's racist to call Canadians effusive pushovers even though "Canadian" is a nationality rather than a race.
And people do exactly that. In the U.K., for example, it's common for people to call people that insult the French "racist."
Language is fluid.
So, I think you can see why people are affronted when someone says "black people cannot be racist" without putting it within a certain context. The implication is that it's not immoral for black people to act denotatively common-usage-racist.
I guess "some" is the keyword here.
The commonly used definition of racism is hatred against people because of their race.
http://dictionary.reference.com/browse/racism
>hatred or intolerance of another race or other races.
A couple of black kids beating a white kid to death because he's white, for example, would be defined as racist under this definition.