If you've been sober for years from drugs chances are you're not going to want to be reminded of it when you'd rather have people focus on your current projects and successes.
I applaud Robert for the way he conducted himself in the interview and the way he exited politely saying: "this is bulls**t! I'm done!" Now, just for context, he did not say those exact words, I am merely paraphrasing.
Anyone else would gone off like a loose cannon and give the press something to print and gossip about them in a poor light. Well, they'll talk about someone in a poor light, but Robert's not the one they'll be panning for the lack of professional courtesy nor demeanor.
Krishnan Guru-Murthy kept going off subject when he should have been asking questions relevant to age of Ultron and Downey Jnr's work and prep work for the movie.
And judging by the number of dislikes on the YT Video (at the time of typing this it stands at 2,452) really shows what fans and other viewers think of the professional conduct of the interviewer.
And people wonder why Channel 4 gets talked about in a poor light?