In fact he's expecting some people will walk out of the cinema when they go to see it.
That's what attracted him to the film in the first place.
"The fact that someone had dared to write a film that was challenging, bold, and potentially offensive to everybody, I thought that was laudable," the star of The X Men and Atonement tells me as we sit on a balcony in London on a hot late-summer afternoon.
Filth is an adaptation of one of Irvine Welsh's most extreme novels (and that's saying something); the story of an Edinburgh policeman called Robbo (played by James) who steals, lies and generally abuses his position, his colleagues and friends.
Robbo is misogynistic, bigoted and racist.
But as the film reveals there's a back story that may change our view of the character.
And the actor hopes you end up feeling for him, just a little bit. "It's about his breaking heart and his breaking soul," he suggests.
"I'm not saying every single person who has those world views is deserving of our understanding, but it's quite fun as a storyteller to be able to go 'you should hate me and you probably hate yourself for laughing at me, but now I'm going to make you feel for me and you're going to hate yourself even more for doing that."
What is clear is that he is having fun playing the part. And if you've got a strong stomach you might have fun watching him.
The Glasgow actor came to prominence in the TV series Shameless where he also met his wife Anne-Marie Duff.
The couple now have a son, Brendan, born in 2010.
Not that that has stopped him working. This year alone he's been seen on the big screen in Danny Boyle's film Trance and London thriller Welcome to the Punch.
He's also made a two-part film with Jessica Chastain called The Disappearance of Eleanor Rigby and soon he's off to Toronto to resume X Men duties.
It's been a good year for him but Filth may well enhance his reputation.
He was so keen to make the movie that he stepped in to help produce it too. He's not sure it's something he would do again.
"If I felt really passionate about something like Filth, then, yeah, of course," he said. "But I'd have to see a real reason why. If you asked me to be a producer on X Men I'd be like 'Why? You've got 20 producers, you don't need it.'
"But they needed somebody on Filth so I was happy to do it. And I also had the time.
"My wife was doing a play and I was looking after the wee fella. I was able to be on the phone when he was having naps."
Does that suggest he's quite handy around the house?
"I'm good at tidying. I'm not very good at cleaning, but I'm very good at tidying," he admitted. "I'm not into Hoovering or getting Mr Sheen out, but I'm good at fixing things.
"But they don't work particularly well, necessarily. I got a boiler working again today."
That's impressive, I say. "It's just making these weird noises," he adds. "That's the only thing."
When he's talking about work James is intense, almost earnest, but ask him about anything else and he's happy to shoot the breeze.
Did he have acting heroes when he was younger?
"Not really. I didn't really think about acting. I never really considered it," he said
"I liked TJ Hooker - William Shatner. I liked the guy from CHiPs, Erik Estrad and I liked Sylvester McCoy in Dr Who. I still quite like Dr Who. It's totally daft but I love it."
He scratches at the raggedy beard he has at the moment.
"I want to turn up at X Men and see if they want it because he's meant to be quite bedraggled when we first meet him," he says of Professor X in the new movie.
If he had a superpower in real life, I wonder, what one would he choose?
"I'd like to be able to make it sunny," he said.
What would you be called then?
Marvel Comics should get in touch.
n Filth opens in Scottish cinemas on September 27.