if you go right, you can't go left at the same time .
you can see it as a balancing the game ; or thinking about the fact that the more you are aggressive and militaristic, the harder is to control your s*** . keeping order require attention , if you want ppl to be soldier or be "elite" of the space, you have to be more focused on them ( and your core planents are more limited) if you just want them to live , you have less controll pressure, and you can have more core planets.
but this may be only MY interpretation .
the fact remain that they seems to want you to choise how you want your empire to be , and not to be evrything .