And if there is disagreement, the source and argument must be considered. If the argument is "policy X says we can't use this" then it should be dismissed as wikilawyering. If a rational argument is presented explaining why it damages the encyclopedia, then it should of course be given consideration.
In most cases, that shouldn't be necessary. We create policies because, in the vast majority of cases, following them is a good idea.
I agree. Following policy should always be the default action. If there is ever a need to violate policy, it is that which requires an explanation.
As for IAR - IAR is for situations which we didn't think of when writing policy. Planning to use IAR for a specific kind of situation is a contradiction, since it is in fact writing a new rule.