I think Stiller's point was highlighting the fact that "serious" actors all feel the need at some point in their career to give their spin on a handicapped person. (Robert DeNiro, Sean Penn, Leonardo DiCaprio, Daniel Day-Lewis, Shawn Cassidy, Dustin Hoffman, Adrian Brody, Tom Hanks, Johnny Knoxville, John Malkovich, etc.)
In the movie, the character talks ignorantly about the challenges and artistry of playing a "retard" in a sense that makes it sound to me like he's making funny of the idiot actor, which is certainly fertile ground.
I understand what you’re saying, dead. Trust me, I believe actors are worthy of any and all ridicule coming their way. That’s the premise that Stiller is sticking to, at least. IOW, actors are so pathetic that they compare to “retards” but no offense to “retards.”
Using his logic it’d be a fair transfer to Robert Downy, Jr’s character of a white actor getting treatments so that he looks black. Would the movie have seen the light of day if “retard” were replaced with “ni**er”, used repeatedly and Kirk Lazarus was told by Tugg Speedman to “Never go full ni**er.” when portraying a black man? Would DreamWorks release a movie poster “Once there was a ni**er...” featuring Downey’s blackfaced character? Would shirts with the words “Never go full ni**er” show up on CafePress and eBay and most likely in a store near you? After all, it’s all a spoof on over the top acting and in good fun, right? No F’n way.
Outside of the clinical useage and in engine tuning I’ve never seen or heard it used where it wasn’t intended as an insult.
I haven’t seen all of the other movies with actors portraying people with disabilities, but I’ve seen a good number of them. They may have been using the stereotypical traits in their acting but not as a means to denigrate someone as Tropic Thunder does.
Obviously with a son with Ds I took special interest in The Ringer with Johnny Knoxville (even though the Special Olympics involve more than just people with Ds) and admit I was apprehensive at first. But I think he and the film did a great job of turning the preconceived negative stereotypes into a positive by showing that physical and mental issues aside they are a lot like you or I and are (seemingly to the annoyance of some) human beings.
Like I said before, I had an entirely different view on PC until my little guy was born. It has run amok. OTOH there are names (words) that have been taken off the table in our society and I don’t see the difference between their usage and intention.