Immigration Explicitly

 Clearly nobody gets it so I'ma spell it out:

 If it's your country, you don't need to justify anti-immigration. If you want to totally ban immigrants, then do. "Because I felt like it," is an entirely valid reason. "I've already decided, just do it." "Will not explain." 

 If it's not your country, your justification is equally irrelevant. Not your decision, regardless of how well-reasoned that decision might be. Even discussing the issue is a waste of time. Secure your shit: find out what the decision is, then plan accordingly. React rationally to what the future situation will be like; don't try to solve it with whining.

 

 Anyway I have to bite a bullet. Immigration is, economically, exactly like population growth. Which is why you should oppose population growth. 

 What's the core mechanism behind Eternal September? Population growth. One of the core reasons behind Roman decay was population growth. One of the core reasons behind modern decay is population growth. 

 There's a maximum level of fecundity your society can absorb. Don't go any higher. If you go beyond it, bust out the death penalty. "Hey Alrenous, what is a raiding party?" "You see, it's an 80th-trimester abortion scheme. Generally eugenic." Everyone loves blood sports. What idiot outlawed them? Celebrate all sorts of activities with enormous fatality rates. Only avoid the ones which often cripple instead of kill, that's ugly.