The Oscar-winning Argo filmmaker revealed that Warner Bros, the studio behind the superhero blockbuster, prepared him in advance for the negative reaction that welcomed his casting announcement.
"[They] gave me a bunch of past reactions to casting and said, 'Are you sure you want to get into this? This is part and parcel of these movies now. There's a lot of active fans with a lot of opinions'," he told EW.
"To me, having been through a certain amount of that, it doesn't really... Everyone's entitled to their opinion. I wouldn't have taken the part if I didn't trust my instincts in terms of the filmmaking. I think Chris Terrio wrote a terrific script. Zack's a great visual director. And there's an interesting take.
"I wouldn't have done it if I didn't think I could do it. I have the benefit of a lot of that understanding. But also, everyone is entitled to their opinion. That's a big part of this international sport. The Fifty Shades of Grey kid or whatever it is. That's sort of become a thing."
Affleck also confessed that he has put himself under intense physical strain for the part in order to get in shape to play the Gotham vigilante, who will go up against Henry Cavill's Superman in the film.
"It's a process that I'll probably have better perspective on when I'm done. I can tell you that every time I do a role, it's the responsibility of an actor to get their physical self as close to the role as possible," he explained.
"And Batman's obviously got a set of expectations that are tough. So I spent a lot of time working out. And it's a far cry from Gone Girl where my character is described as 'puffy and hungover'. I want you to know I worked equally hard at both!"
Batman v Superman: Dawn of Justice will open in cinemas on March 25, 2016. Watch Digital Spy retrospective video on Batman's 75-year history below: