When you have zero incidents using the temporary process people will automatically start to assume it’s due to the temporary process, and nobody will want to take responsibility for taking it out.
I agree with the implication, but don't think this applies here. The scenario here is a safety net, i.e. something that visibly "catches" errors, at a cost. If you have zero incidents "caught" during the evaluation period, then the evaluation result is that the cost isn't worth paying.
Obviously if you're planning to implement a vague deterrent-style solution which you have no means (or intent) of evaluating just to check a box, you're better off not doing it.
When you have zero incidents using the temporary process people will automatically start to assume it’s due to the temporary process, and nobody will want to take responsibility for taking it out.