maggie, I think arguments like that really neutralize the critical thrust of the concept of racism. If cops target ethnic minorities for systematic harassment because of "profiling" (read: racist stereotypes) or shoot a Black man on the assumption that he might be a suspected criminal - that is racism pure and simple. Claiming racism in such situations has a critical thrust because includes a specific institutional context that takes advantange of and reinforces individual attitudes toward minorities.
On the other hand, if we take the fucked up rationalizations of deranged or alienated individuals for their face value (i.e. as a true motive of their actions) - that is essentially ignoring the specific institutional aspect that makes racism a socially dangerous thing. That sounds like bourgeois "mentalism" (i.e. actions being guided by ideas) rather than marxist materialism (i.e. ideas being a reflection of material/social conditions). Bringing that institutional context back in by cliches like "the entire US society is racist" furter obfuscates the issue.
To be empirically meaningful, a concept must denote a class of objects that can be effectively distinguished from other classes of objects. All-embracing concpets might be full of emotive connotations, but are generally devoid of empirical meaning. That devalues them as tools of social critique.
Wojtek