I think what he was trying to say is that you don't want to overact when you're behind the cape and cowl. An outfit like the Batsuit already exudes a tense and ominous vibe -- it's kind of built-in. While there's certainly nothing wrong with Batman having a temper tantrum on occasion, I've always been more partial to iterations of the character where, saying very little, he uses psychology to play upon the fears of criminals. In so doing, he wins the battle before it's even fought. If that's what Ben was going for in his portrayal, I'm all for it.