How understandable/sympathetic is this antagonist's motivation?

Okay, my villain is basically an angel (or more technically, a member of a race of untainted human souls that get repurposed into newer, stronger bodies in another dimension after their human body on earth dies. Their only real rule is that direct murder is an instant death penalty.). He's the #2 man for that dimension's ruler, an absurdly powerful reality warper.

Now, this ruler is so powerful that he's incapable of setting foot on earth without killing all life on it. He has an amulet that not only contains his powers, but keeps them in check. What this means is, after a particularly potent display of power, the amulet would cut off his power and he'd be rendered powerless for a while. This allows him to both limit himself, and gives him the ability to go to earth for short stretches.

The ruler had a son (the only denizen of that dimension to ever have one), and an evil counterpart to the ruler appeared on earth, threatening to first enslave all life on earth, then to attack their dimension. The ruler could've handled him, but the son begged him not to (since his appearance on earth would kill all life on it, and his son was a massive fan of humans.) and implored his dad to send him instead. The ruler agreed, and his son got into an epic duel with the evil one.

The two realized they were evenly matched, so they simulataneously seperated each other's spirits from their powers and sealed them away on earth. The ruler went mad at this (having lost his beloved son) and turned his back on the world. forbidding anyone from ever looking at it or interacting with it ever again.

Now, the villain's motivation is that the dimension where the angels reside is getting so cramped that certain angels are being forced to ritualistically kill themselves just to free up space. The villain plans to trick the ruler into going down to earth (razing it to the ground in the process) then getting him to use enough power to be forced into depowered mode, then killing him while he's powerless, therby taking control of the amulet. He would then use the empty earth as extra living space for his kin. He thinks that any decent people living on earth would be turned into angels in the process anyway, and since angels as a general rule can't procreate, there's no chance of further population increases after all the humans are dead.

Is this an understandable/sympathetic motive? (on a scale of 1-10, say)

I think it's understandable and sympathetic, but incredibly sneaky and cruel at the same time. Why not use a different place?

5/10.

They kinda only have the two dimensions to choose from.

Oh wait, I think I'm missing something, why is the place where the Angels live getting cramped? Was it simply always cramped, or how is it getting more cramped?

Otherwise, I think it's okay, I'm curious though is your plot only about the angels or are humans involved as well?

@Ginger: Seems like a perfectly decent motivation to me.

@bread because any decent human automatically get reincarnated as an angel when they die.

Couple with the fact that angels have elf immortality... (can die, but not from old age)

and the story is focused on certain humans that have shards of the ruler's son and the dark one's power in them.