The way I saw it, was the guy was infuriated with how it all went down, and let rage get the better of him.
Should he have calmly stated that he didn't agree with the situation? Yes.
He probably got upset with the initial event, stewed a second on it, then the reaction to the event just made him snap.
But again, he didn't fly off the handle and start hitting anyone. He made a stern claim to the FA to bring him down a peg.
That's when the FA should have realized that his actions, whether right or wrong, were obviously perceived as being wrong. He's got a crying woman with a baby and a man yelling at him for it. Since he's being paid, on the clock, and its his job, he should have known way better than to run down the aisle turning up the situation. A simple, even if empty, "im sorry sir" would have done wonders. He should have just tried to calm everyone down. The FA was so enraged about taking the stroller that that man's comment set him off like that? I'd take that passengers rage any day over that FA's. Two wrongs never make a right. In my mind, one guy is an employee, one guy is not. I put the onus on the employee.