[mkaziz]

Addressing your first point: the problem is that they're stagnating /now/. They don't have the means or will or resources to deal with their problems. There's not enough labour to support the elderly population.

I'm sure they can decrease inflow at an appropriate time, but for now, they need fresh blood and fresh ideas.

[thevardanian]

They are "stagnating now" but the long term problem isn't solved even with immigrants. So the point is that humanity itself needs to find a sustainable solution. They definitely have the resources to deal with their problems, they just don't have the labour to utilize those resources. For example migrant labor is definitely a solution that Japan is working on.