We don't really run into these guys until the end of the movie when they come out in full force to beat up on a bunch of children. Hey, we didn't say they were nice people.
In the film, the group is led by Lucius Malfoy and he's on a mission to do one thing and one thing only—get that prophecy for Voldemort. And he is not gonna let his psycho sister-in-law, Bellatrix, mess this up:
LUCIUS MALFOY: Now, hand me the prophecy.
HARRY POTTER: If you do anything to us, I'll break it.
BELLATRIX: He knows how to play. Itty, bitty baby. Potter[…]
LUCIUS MALFOY: Now, let's everybody just calm down, shall we? All we want is that prophecy.
HARRY POTTER: Why did Voldemort need me to come and get this?
BELLATRIX: You dare speak his name? You filthy half-blood!
LUCIUS MALFOY: It's all right. He's just a curious lad, aren't you?
That's right. Everyone just calm down. We're half expecting Lucius to tell Bellatrix to go wait in the car while he murders these children on his own. It'll be way less drama.
The Death Eaters might be a mixed bunch, but they all know one thing, failing to deliver for Voldemort is not an option. Bellatrix has passion and devotion to the Dark Lord, but Lucius has the ruthless drive to get the job done.
That's why Harry's right when he says Voldemort doesn't have any friends. The Death Eaters aren't people Voldemort cares about, they're folks he uses to get what he wants. They're so disposable that maybe they should be wearing red shirts instead of black robes.