That's actually probably the easiest way to filter for productive immigrants, actually. Ask them if they would prefer open borders or tightly-controlled borders and then let only the second group in.
😂 4D chess. 

 True enough, but perhaps not sufficiently so to prevent social welfare being useful politically.

Social welfare here is far from universal; there are interviews, tests, social worker's discretion, and, for many categories, a race requirement. (Germany may be different.)

It makes perfect sense when you view social welfare as a patrimonial system for vote-buying at the lowest cost. (Just as industry policy here is mostly grant-laundering at high cost).

Elites can still use social welfare to buy new immigrant voters as long as existing citizens can be excluded from it.

There is a level of economic disarray at which this will cease to draw, but the regime's other vital functions have probably imploded before that.

I encourage both tax avoidance and tax evasion to accelerate this, I admit.