Intriguing points, CotE. I'm perhaps being a little too set in my ways, but this:
Originally Posted by Child-of-the-Emperor
But apart from that we don't truly know that they are aiming for.
seems, again, quite accommodated by Ch7 [i]Legion.
That is: their big aim is humanity's survival and that humanity (or the Alpha Legion) is involved in controlling it. No 'God-Emperor', no Horus, no Chaos Gods and, laughably, certainly no aliens.
Simply: the Alpha Legion aren't willing to sell out humanity as a whole. They'll sell out the Emperor. And Horus. And the cabal. But the species?
They won't even let themselves be in complete control...because there are always other 'heads of the hydra' which are willing to argue or intervene. Even by 40k, it could be argued, they're still doing that. By 40k, really, are they much
worse than the 'bad end' of Radical Inquisitors? I mean, sure, Voldorius is a right twerp, but contrast the work of Bronislaw Czevak: in cahoots with daemon hosts, witches, aliens and renegades of any description...yet he's perhaps one of the most gloriously, unashamedly 'free thinking' and 'profoundly visionary' characters out there. To say the character's principled is something of an understatement.
But both Czevak and the Alpha Legion have an odd transcendence of a story's goals, or even a person's goals. It's somewhat difficult to articulate.
Sorry, I'm rambling. I'll get a point one day, probably.
But it all rests on Ch7 being 'true'. (If it's all lies or theatrics, well...anything goes.) As if it's 'true', then as long as the Alpha Legion are calibrated right to be 'self-organising', or indeed, like a hydra...then they can operate well enough to properly have humanity walk the knife edge...hopefully...