If he didn't know Gladio, Ignis would've backed down with a quickness as there was no need in poking the bear so to speak. He listened to the shield and all he could do was shake his head. Let him loose? Well he was right in the fact that there wasn't anywhere to go and letting Gladio do such a thing was always beneficial back home. It was good to let him have space to breathe, think and calm down.

Here there wasn't that benefit.

Years of knowing the man before him made Ignis not argue. He got closer to Gladio and couldn't seem to find the words he wanted to say. So all the shield got was an apologetic sort of look. He knew Gladio was doing the best he could with what he had and doing the best he could. It was he who failed the shield, not the other way around.