My thought is that someone does not become a Death Eater by merely being a follower of Voldemort, anyone can agree with Voldemort, anyone can do the grunt work for him, campaign for him, fund him, but to earn his respect and become a Death Eater? There MUST be more to it. They must actually Desire what he Desires, fully, and comprehend what that actually entails and what they must do to get there- they must know, and be willing, to kill and torture in his name, to tarnish their souls forever to get close to him.
They have to be willing to pledge their Mind, Body and Soul to him, and his Cause.
The Death Eaters operate as a secretive cult-like gang, where they must have committed the most heinous acts to even earn that title. It is my view that there is an Initiation Ritual that requires the new would-be Death Eater to capture and murder a muggleborn, and consume the blood, flesh, and heart of their victim, presided over by Voldemort himself and his closest, most trusted allies, and that this Ritual would have life long consequences for the initiate- a permanent Blight over their soul, perhaps even hunger for human flesh and blood that cannot fully be extinguished within them, but for the new initiate this act of utmost barbarism and evil is worth the consequences.
In exchange for their humanity they are bestowed secret knowledge, powerful magic, and personal mentorship from the Dark Lord himself, and the promise of being rewarded handsomely in the future once the Dark Lord's plans are fulfilled, and his conquest of Magical Britain is certain- and these rewards will ofcourse be things like powerful positions within the new government, immense wealth and status within their new society, exultation and admiration, and the chance to drive their enemies beneath their feet. They have a deep desire to radically change magical society, and are willing to kill, torture, and maim for it.
I've always felt that those within Voldemort's inner circles must have proved themselves in some way to be there- wealth and blood status cannot be the only factors. They must have shown themselves to be exceptional, and if not magically exceptional than at the very least ready and willing to commit themselves to him even at their own detriment. I feel as though Voldemort would accept no less from his Death Eaters, that they MUST prove it, that they must bind themselves to him, and eachother, in ways beyond the superficial dark mark- something that they cannot come back from, that to become a Death Eater they have to truly plunge themselves into the depths of evil from which there is no coming back.