This would be grounds for complaint if your teaching load was significantly different from that of your colleagues and there were no field-specific reason for that to be the case. It all depends on circumstances though -- 3 intro courses and a grad seminar might be equivalent to four 3rd or 4th year courses. But if you really object to all the intro courses (and not everyone does -- if I have one intro course prepped, and TA graders, I like to hang on to it!), why not talk to your chair about your schedule? Or bring up the issue of coure allocation procedures in a department meeting?
Is your teaching load significantly different from that of your colleagues?
It sounds like we are talking about separate things. I get the impression that the "intro" courses you are talking about are all very large lecture classes that may or may not be taught with the assistance of TAs. Not all my intros are large and we have no TAs. A course counts as one course, regardless of size. My intro course of 30 counts the same as my intro course of 150. However, none of our upper division classes are EVER over 50, and several are capped below 20. That means two faculty with identical teaching "loads" can teach wildly different numbers of students in the same year (e.g., 500 vs. 175) and this is considered "equitable."
My perspective--and I guess my question--was what is so objectionable about intro courses (controlling for course size, etc.)
qua intro courses? It sounds like you are saying nothing is objectionable per se, only that structural differences can create an inequity (which I would agree with, but about which I can do nothing). Does that fairly reflect what you were trying to say?