"-ism"?

[alixtii]

What do people mean when they say that "-isms" are bad? Are they just talking about systems of injustice, like racism, sexism, heterosexism, classism, ageism, ableism, anti-Semitism, et cetera? Because, you know, "feminism" ends in -ism. (As does, for that matter, "Judaism" and "Hinduism" and whatnot.) Or are they making a claim that all ideologies are bad? Which I can almost see, from a sort of neo-Marxist perspective, only . . . "Marxism" ends in -ism, too. (As does "positivism," the ideology which most violently represses its own ideological character, and of which many brands of Marxism are subtypes.)