He tells HuffPostUK, "Everyone's been asking me, how was it to do the gay scene? It's like they're, to be honest, about nine years old. They're really shocked by it, but I don't think it's shocking."
Radcliffe plays a young Beat poet Allen Ginsberg, in this rite-of-passage tale, concentrating on his infatuation with fellow New York student Lucien Carr, played by Dane DeHaan. Their intense relationship goes horribly awry, when Carr is charged with the murder of his 'benefactor' David Kammerer, played by a volatile Michael C. Hall. As you can see, there's a lot going on, which is why Radcliffe remains bemused by people concentrating on just what's happened to their favourite boy wizard...
"In 2013, people are talking about a gay sex scene. Is it really that shocking? Russell Crowe had a really explicit gay sex scene early in his career. It's a weird, odd double standard.
"I've done Equus. I've played a character who had a religious and sexual worship of horses, and I got less questions about that than this."
So what IS the most shocking thing he actually does in this film? He ponders...
"Probably be manipulated by someone after they've committed a murder, oh, and throw some books around."
What's certain is that Radcliffe has, once and for all, left behind his boy wizardry, although he seems less sure of this than me... "we'll see"... Does he feel he has to push for more extreme roles than lesser-known faces?
"It wasn't a case of having to go to extremes," he explains, striving for accuracy in his reply, but acknowledges, "You have to show more range than people have seen before - an American accent, a different period - but it wasn't about having to find something to shock people. Because, unless the film's good, shocking does nothing."
"Part of the joy of this film is that they're talking about changing the world, completely unironically, with unabashed high-flung ideas about themselves," explains Radcliffe, who, it is clear, has none of the complacency that you might expect of arguably the most successful young actor of his generation. He remains palpably, energetically curious, with, I'm sure, the best of his work ahead of him... when did he decide?
"I was 14," he says straight away. "I realised, this is something I want to do for the rest of my life, how do I get better at it?'
"It was watching Gary Oldman, David Thewlis, seeing the sense of abandonment with which they threw themselves into their roles, and seeing what it gave them. I thought, I want a piece of that."
'Kill Your Darlings' is in UK cinemas from Friday 6 December. Watch the trailer below...