In that line they thought that they were showing their allegiance to the state. They did not want to be committing a act of treason. They were taking what pilate said at face value. Isn't there more to that question that Pilate asked? Isn't there a hidden meaning behind it? What can we learn from that statement?
There's definitely more to the question. Figuratively speaking Pilate is testing their will. Pilate knows that Jesus is innocent. Pilate knows the hearts of the chief priests. Although even more troubling is with that knowledge Christ is still sent to Golgotha.
The every day disciple of Jesus Christ can also ask Pilate's question. The question measures exactly how one feels about Jesus Christ? Many questions are answered by where people put themselves on that spectrum. Are you willing to listen to the spirit? Do you except the atonement?
Yes, it's true that the chief priests were so harden in their hearts. They could not bring themselves to believe that Jesus was the Christ the Messiah. They could not disapprove him. So they had to kill him by false pretense. They were threatened by the Carpenter. Jesus was drawing crowds to him by the thousands. So, they had to put an end to him. The hymn comes to mind "Whose on the Lord side too, now is the time to show" it's important to recognize where to stand when picking sides. Where exactly do you stand? Where exactly is your heart? Are you willing like the chief priests to deny the Christ?