In very specific academic contexts racism is defined on an institutional/societal level.

No it's not. institutions and societies are involved but it's a phenomena that exists on multiple levels, including that of the institution and society but also at the individual level.

Inside of those very specific contexts white people in western countries cannot experience racism because they historically have controlled the institutions necessary to implement it.

Actually, no. The idea is that they can't experience racism because the whole-system phenomena (as parsed on different levels which all are directly related and contributory to one another) supports their supremacy. History plays a role but the meat of the argument deals with things as they stand right now.

Idiot teenagers and first year college students learn about racism, don't understand the subtle differences between racism and racism as defined in the dictionary and what the word means to most people in most situations. This is the end result.

Typically, I view people that don't go to college and rely on dictionaries as if they were bibles as the idiots. I may be wrong here though. I, at least, am open to the idea of not being wrong. I also don't make it a habit to argue experts down.