Interplanetary immigration is expensive. Not horribly so, but you're looking at a few kCr per body as steerage, and you're buying a lot of bodies if you're trying to affect Pop codes.Your thoughts?
It's also disruptive. Culture and language differences need to be accounted for. Traveller handwaves this a lot, but it should matter. It also creates a community that may be isolated from the host-world's culture, and which may form a power bloc that's at best imperfectly aligned with that of the host world. And keep in mind that the immigrants are likely intended to slot into lower-paid jobs or economic sectors, which gives them a potential grievance against the host world.