Thinking we shouldn't change words without changing the dictionary is...its not a particularly sustainable position. There's a debate in dictionary-maker circles between prescriptivism
. It's precisely as interesting as the phrase "debate in dictionary maker circles" makes it sound, but in brief its whether dictionaries are/can be/should be laying down rules about how words must be used (prescriptivism) or reflecting how words are actually used (descriptivism).
I bring this up because the point is that not even dictionary makers
agree that trying to change words without changing the dictionary should be discouraged. Generally, the presciptivist viewpoint doesn't gel with reality because people don't take their usage from dictionaries. Look at local dialect words for example.
Essentially, I don't think thats a particularly good viewpoint to hold in the long term. Look at how people use words then check to see if the dictionary has been updated to reflect that yet. Doing it the other way round is incredibly reductionist. Words change meaning and they do so faster than new editions of dictionaries are economically feasible.
Further, "racism" hasn't been around for centuries, its been around since the thirties. Literally, albeit not by much, within living memory - there's no long standing tradition to overthrow. It's a new word.
All that said, though, it doesn't actually matter because if you did go to the dictionary (depending heavily on which one you chose) you may well find that it is a given definition. Wikipedia's section on definitions of racism
- and note the plural there - does a pretty decent job as an intro.
EDIT: Grammar is hard.