John 11:48

If we let him thus alone, all men will believe.

They take it for granted that his miracles were calculated to produce belief. They also held that the people would regard him the Messiah and would rise in insurrection, or raise tumults that would induce the Romans to interfere.

The Romans... will take away our place and nation.

The Romans were already there, for Judea was. Roman province, there was. Roman governor, and also. Roman garrison was stationed in the tower of Antonia overlooking the temple itself. But they had their place still, were priests with great revenues, or members of the Sanhedrim with great power. If there were seditions they might lose "their place," as they did. generation later. To take away "their place" would be to destroy the ecclesiastical organization, while to destroy the civil organization would be to take away "the nation" in the sense they used the term.