The willingness of people to accept those that govern depends on how much trust they place in the validity of the vote. Lessening the security of voting or allowing it to remain insecure lessens the capability of government to proceed with the approval and cooperation of the people. If they cannot trust that their vote is secure, they cannot trust that their government represents them.

Government exists by the grace of those who are governed. THIS is the core argument. Focusing on conviction rates for vote fraud or whether or not it could in theory flip an election is meant as a distraction. Once they have you distracted on numbers, they don't have to say that non-citizens should vote. They don't have to say that allowing room for fraud is good (because it benefits them).