How is this defensible? Asserting that by virtue of their powerlessness black people can't be racist? That's a statement that should offend anyone, especially black people.
Racism, sexism, etc. are characterized by the desire to damage a certain group while propping up another by making broad-scoped and baseless inferiority/superiority statements, often followed up by aggressive actions. It's not necessary for one group to be "in power" for this to happen. Racism in cases where minorities are the perpetrators is exactly as unacceptable as in any other circumstance and people who defend that should be called out for it.
In short, and conveniently looping back to the actual topic at hand: behaving like an asshole is never OK.
Racism, sexism, etc. are characterized by the desire to damage a certain group while propping up another by making broad-scoped and baseless inferiority/superiority statements, often followed up by aggressive actions. It's not necessary for one group to be "in power" for this to happen. Racism in cases where minorities are the perpetrators is exactly as unacceptable as in any other circumstance and people who defend that should be called out for it.
In short, and conveniently looping back to the actual topic at hand: behaving like an asshole is never OK.