I don't like the way Wallace & many others suggest irony and sincerity are dichotomous. They're part of a cycle. Wallace suggests that irony has run its course and broken down everything it needs to break down (which makes me think that he's channeling Fukuyama: Seinfeld destroyed communism so now we can just be wholesome all the time), but the world is full of shitty ideas that need to be challenged, and an ironic stance is useful to the point of almost being necessary for challenging certain kinds of ideas.
The ironic stance is like the veil of ignorance: it allows us to observe ideas out of context and criticize them for their form rather than their effect. This is so powerful that it's almost equally capable of shredding good ideas as it is of shredding bad ideas. But, without it, all we have is identity politics without intersectionality.
Some problems are hard to see without stepping outside yourself and looking unsympathetically at the situation. Other problems are hard to see without empathy grounded in experience. Ignoring either set of problems leads to awful results, because the world is a mish-mash of soulless machinery and fragile human guts and understanding only one leads to breaking both.
Another nuance here is that there's no such thing as ironic enjoyment. If you're feeling something, that feeling is sincere, even if you feel it as the result of actions taken from an ironic stance. Someone whose self-conception is related to irony (which I think is the core criticism of New Sincerity: lifestyle irony, rather than an ironic stance in of itself) will see sincerity through an ironic lens, but while delusional posuers may be annoying they can hardly be considered a real threat. Basically, any position taken ironically is at least partly genuine and should be considered as genuine, because the idea that an ironic stance excuses actions taken under it has never held water.