Which fallacy is committed in the following statement? "Nobody has ever proved that immoral behaviour by elected officials erodes public morality. Therefore we must conclude that such behaviour does not erode public morality."

The argument concludes a claim is false merely because it was never proved true, an appeal to ignorance.

The premise states only that no one has shown immoral conduct erodes public morality.

Failure to establish a proposition is not the same as establishing its opposite.

The absence of a proof leaves the matter open, not settled in the negative.

Here the missing proof is wrongly treated as positive ground for denial.

Drawing a conclusion from what is not known is argumentum ad ignorantiam.