These lines from a discussion by Marshall Berman of the Communist Manifesto identify a critical dividing line that runs through the history of the left:
Marx hates capitalism, but he also thinks it has brought immense real benefits, spiritual as well as material, and he wants the benefits to be spread around and enjoyed by everybody, rather than monopolized by a small ruling class. This is very different from the totalitarian rage that typifies radicals who want to blow it all away.
The point that Marx looked forward to a line of social and political progress vis-à-vis the capitalist society he criticized betokens a building-upon rather than blowing-away cast of mind. And individuals and organizations of the left have too often lost sight of that. They have done so particularly in their critiques of so-called 'bourgeois' democracy. In this sphere, as more generally, unless socialism can at least retain, and at best improve on, the virtues and protections of liberal pluralism it isn't worth supporting. (Via.)