The critic argues that disrespectful comedians are popular precisely because we currently value respect highly. But the argument doesn't depend on the traits of audience members who enjoy disrespectful comedy, making (A) unnecessary.

We can illustrate this using negation: if (A) is false, and people who enjoy disrespectful comedy still value respect highly, that doesn't harm the argument. Because negating (A) leaves the argument intact, it's not necessary.

Disrespect “often” makes for successful comedy, but the critic doesn't need to assume that disrespect is the only way for comedy to be successful. Other forms of comedy being successful wouldn’t undermine the conclusion, because that wouldn't take away from the critic's explanation of why disrespectful comedy is successful.

We already know from the stimulus that disrespectful comedians are generally popular, so there’s no need to assume that anyone disapproves of comedians’ disrespect. The nuance of exactly how popular these comedians are doesn't make a difference to the argument.

This must be true in order for the critic’s explanation to work, meaning (D) is necessary to assume. We can see this using negation: if people did always succeed in living up to their ideals, then there would be no “failings” to exaggerate, meaning the critic's explanation for why disrespectful comedy is popular falls apart.

The conclusion is about the current popularity of disrespectful comedy, so nothing needs to be assumed about the past. We don't know whether disrespectful comedy is more or less popular than it used to be, and either way it wouldn't matter to the critic's argument.