Random thought: Dumbledore isn't a complete moron that refuses to properly punish Death Eaters, he's just as piss poor with sharing information as always.
In this case, the Dark mark is a perverted protean charm applied to the DE's very soul and anchored, quite literally, their flesh (the tattoo). The charm being applied to their very soul means it follows them unto death- lending Voldemort either A: the strength/magic/etc of their old body, a connection to the latent magic of the afterlife, whatever.
Long story short, every time you kill a DE, Voldemort personally gets stronger, though maybe only until that specific soul is reincarnated, which may take a while given that the soul is likely in 'time out' for their actions on the mortal coil. Regardless, Dumbledore can't let people kill off DE's.
As a bonus plot point, if their soul isn't wiped clean of its bonds upon reincarnation, you may have a baby that's born with a connection to the dark lord- an unstable one, given the lack of the tattoo to stabilize it, but it could bring about some really interesting character development and philosophy. Regulus would be a good soul to use- he died before Harry was born, and his penance would likely be shorter given his actions, so it could potentially be a child only a little bit younger than Harry- but still 'marked' by voldemort.
In this case, the Dark mark is a perverted protean charm applied to the DE's very soul and anchored, quite literally, their flesh (the tattoo). The charm being applied to their very soul means it follows them unto death- lending Voldemort either A: the strength/magic/etc of their old body, a connection to the latent magic of the afterlife, whatever.
Long story short, every time you kill a DE, Voldemort personally gets stronger, though maybe only until that specific soul is reincarnated, which may take a while given that the soul is likely in 'time out' for their actions on the mortal coil. Regardless, Dumbledore can't let people kill off DE's.
As a bonus plot point, if their soul isn't wiped clean of its bonds upon reincarnation, you may have a baby that's born with a connection to the dark lord- an unstable one, given the lack of the tattoo to stabilize it, but it could bring about some really interesting character development and philosophy. Regulus would be a good soul to use- he died before Harry was born, and his penance would likely be shorter given his actions, so it could potentially be a child only a little bit younger than Harry- but still 'marked' by voldemort.