There's an interesting appraisal by Morris Dickstein of the career of Irving Howe in the December/January edition of Bookforum. At one point, Dickstein recalls his youthful "amaze[ment]" in the mid-1960s that Howe "could write a sympathetic essay on Berkeley's Free Speech movement one year, then publish a furious onslaught against the New Left barely a year later".
I take it the "furious onslaught" Dickstein refers to is Howe's 1965 essay "New Styles in Leftism" (happily made accessible in 50 Years of Dissent edited by Nicolaus Mills and Michael Walzer). And I don't think Dickstein need have been amazed, for what Howe was marking in that essay was a distinctive mutation in the American New Left, measuring the distance, as it were, between the Port Huron statement and the writings of Herbert Marcuse; between a left that regarded itself as the legitimate heir of the liberal tradition and a left that regarded the values of that tradition as so many dispensable "fetish concepts" (Marcuse, "On the New Left", 1968).
Incidentally, John Deigh speaks up for the Port Huron statement in a post at Left2Right. He's responding to some remarks made by Christopher Hitchens in a review in the New York Times. Hitchens says this about the Port Huron statement:
[I]t was in essence a conservative manifesto. It spoke in vaguely Marxist terms of alienation, true, but it was reacting to bigness and anonymity and urbanization, and it betrayed a yearning for a lost agrarian simplicity. It forgot what Marx had said, about the dynamism of capitalism and ''the idiocy of rural life.''
Deigh disputes this reading:
The Port Huron Statement is about democratic ideals. It's about America's emergence from World War II as the beacon of those ideals and about our country's failure to be faithful to them.... [The authors'] concerns had more to do with Thoreau's "mass of men [who] lead lives of quiet desperation" than anything like alienated labor in Marx's sense. They owed their ideas to Hobhouse and Dewey, not to Marx, who had no presence in their thought, vague or otherwise. And the dynamism of capitalism was a given, as it must be in any twentieth century political tract.
ADDENDUM: Reading Howe's introduction to a 1970 collection entitled Beyond the New Left, I came across this passage which supports the point made above:
The first [phase of the New Left was one] of populist fraternity, stressing an idealistic desire to make real the egalitarian claims of the American tradition.... The main slogan of that moment -appealing but vague- was "participatory democracy." For those of us committed to democratic socialism, this first phase of the New Left was, despite occasional tactical blunders, a profoundly welcome and promising reinvigoration of American political life....
The second phase of the New Left signifies a sharp turn away: away from fraternal sentiment and back to ill-absorbed dogma, away from the shapelessness of "participatory democracy" and back to the rigidity of vanguard elites, away from the loving spirit of nonviolence and back to a quasi-Leninist fascination with violence....
[P]erhaps most distressing of all, the liberal values of tolerance and respect for the rights of opponents were sneeringly dismissed in accordance with the formulas of Herbert Marcuse.