]This picture is not where he sustained the injury but I believe RDJ was doing this scene himself
It's pretty crazy there were none of the main actors were injuried on Avengers, but RDJ got hurt in IM3. I guess we should be thankful that Joss Whedon is probably a safety nazi on set.
Sigh, the facepalms you create...
RDJ is a fully grown man more than capable of making his own decisions and certainly has earned the weight to throw around to get to make that choice. If he wanted to do a stunt by himself, by-damn who's going to tell him no? He's Robert Fucking Downey Jr.! If they don't agree to his demands who's their second choice?
So he does a stunt (or whatever) and twists his ankle. Big deal. He spends a day or two off his feet with some ice on it, the production switches to second-unit stuff or scenes without him, life moves on.
No need to declare fail on the entire industry, this particular production or to start thinking of delays in the release because a 50-year-old man wanted to do his own damn stunt.