I'm super confused by what point you're trying to make.
1. Who is suggesting that immigration just be universally let everyone in? I didn't come close to saying that. Immigration is always case by case. How else would it be done?
2. But "culture clash" is a silly, racist, xenophobic thing to try to base it on. It makes very little sense.
I'm making a point about "number of visas allowed per year." Any country complaining about birth rates, should increase it.