Both Kevin Drum and Amanda Marcotte, in slightly different ways, think progressives need to learn to have more fun. Nobody likes a coalition of sourpusses.
Now, at one level, the charge that progressives only speak in terms of the dark and dire is unfair. For example, Drum gives as one example of "grim and joyless" progressive politics the assertion that "Nobody is 'illegal.' We should welcome hardworking folks from south of the border. Unless you're a racist, that is." But this is a politics that can and often is expressed in positive terms (it has "welcome" right in the tag!). Celebrating immigrants and embracing them as full members of the community is the stuff of many a heart-warming viral video. Certainly, progressive immigration talk has its share of downer narratives ("children in cages"), but on the whole the framing is far more upbeat on the progressive side, where it is mostly celebratory and about inclusion and growth -- certainly as compared against dark GOP mutterings/bullhornings about stolen jobs and foreign invasions and great replacements.
At another level, anyone who spends time in a largely Christian society quickly learns just how many people do love a bit of self-abnegation. A little masochism goes a long way, and clearly there is pleasure to be taken (and people take great pleasure) in forms of performative self-flagellation that are the hallmark of at least some forms of progressive political behavior. The line between pleasure and grimness isn't quite as sharp as we think it is.
That said, I think there is something to the notion that progressives are maybe not giving joy the credit that it should get -- perhaps on the theory that anyone who has the temerity to express joy is disrespecting all the terrible oppressions and mistreatments that afflict various marginalized groups in contemporary society. But this approach just doesn't resonate with people who even or perhaps especially in dark times want to see and feel opportunities for happiness.
Take the Olympics. I'm on the record as a strong Olympics booster, even as I'm fully cognizant of all of the very compelling critiques of the Games: they're corrupt, they displace people, they're fig leaf for authoritarian oppression, and so on. All of which is, indeed, true, and I don't deny the weight of those critiques. But sometimes it seems as if the persons making those critiques act as if there is nothing of weight on the other side of the ledger -- it's this parade of terribles on one side against meaningless frivolity on the other, such that only the truly self-indulgent or bubble-headed could possibly find value in it. No. No, no, no. The Olympics represent a rare -- perhaps singular -- example of the entire global community coming together in one place for the primary and fundamental purpose of doing something fun and joyous. That is a great thing, and there is virtually nothing else comparable to it.
Recognizing that doesn't mean that there aren't important proposals for how to reform the Olympics to mitigate or eliminate its darker sides, it doesn't even compel one to weigh that good as superseding the aforementioned evils. But there needs to be recognition that the good, is a good; that the joy the Olympics creates can and should count for something, and one is not showing oneself to be a self-absorbed dilettante if one enjoys something meant to spark joy. The inability to recognize the joyousness of the Olympics -- to solely see it through the lens of the dark and the grim and the dire -- is not healthy, and for most people it's not relatable.