I wonder if Malcolm X ever considered that alienating white liberals decreased their ability to help his cause.

Did you look up the context of this quote? Because here, read the whole thing:

The White liberal is the worst enemy to America and the worst enemy to the Black man.

Let me first explain what I mean by this White liberal. In America there’s no such thing as Democrats and Republicans anymore. That’s antiquated. In America you have liberals and conservatives. This is what the American political structure boils down to among Whites. The only people who are still living in the past and thinks in terms of “I’m a Democrat” or “I’m a Republican” is the American Negro. He’s the one who runs around bragging about party affiliation and he’s the one who sticks to the Democrat or sticks to the Republican, but White people in America are divided into two groups, liberals and Republicans…or rather, liberals and conservatives.

And when you find White people vote in the political picture, they’re not divided in terms of Democrats and Republicans, they’re divided consistently as conservatives and as liberal. The Democrats who are conservative vote with Republicans who are conservative. Democrats who are liberals vote with Republicans who are liberals. You find this in Washington, DC.

Now the White liberals aren’t White people who are for independence, who are liberal, who are moral, who are ethical in their thinking, they are just a faction of White people who are jockeying for power the same as the White conservatives are a faction of White people who are jockeying for power. Now they are fighting each other for booty, for power, for prestige and the one who is the football in the game is the Negro. Twenty million Black people in this country are a political football, a political pawn an economic football, an economic pawn, a social football, a social pawn...

Politics have changed a lot since then, of course, but I think his message is pretty clear, and still valid. If you're the kind of "white liberal" who doesn't give a shit about Black rights except when you need Black votes to get your candidates elected - and there are tons of those holding office in the Democratic Party today - then you are an enemy of the Black man and America as a whole.