The Sacred Canopy," "The Heretical Imperative," and "In Praise of Doubt"), he lamented how unhappy most mainline Protestants seemed to be. In the guise of being prophetic, he noted that they always seemed to be always complaining about how bad the world was without acknowledging how good it was (Sure glad he's smiling in the picture). Hence his remark about liberalism with a frown.
I know what he means. Although the world's hardly perfect and is (and will always be) in need of redemption, it's better than it was decades, centuries, and millennia ago, but you wouldn't know it listening to some mainline Protestants. To be sure, there's still a lot to do in terms of civil rights, but does anyone honestly believe that 50 years ago an African-American American Idol finalist from Louisiana would have been honored by his hometown ("How Far We Have (Over) Come")? And as Steven Pinker has demonstrated with rigorous empirical analysis ("The Better Angels of Our Nature"), today's world is far less violent than it once was. For example, although we lament the violence of American society, especially after the Newton tragedy, the probability that one would die a violent death (at the hands of another person) in a hunting and gathering or agricultural society was between 15% and 25%; today it's less than 1%. That's not an insubstantial difference.
However, you wouldn't know it if you only listened to some mainline Protestants. Some simply aren't happy unless they're complaining about something (and wearing the requisite frown on their face). Thankfully, this isn't true of the mainline church my wife and I attend (although there are a few exceptions), which is one of the reasons we like it so much. I'd like to think that our church isn't an exception. My concern is that it is.