Either you can have a welfare state and restricted borders or no welfare state and open borders, as for me I'll choose the former.
How do you explain Europe? For all of the Schengen zone's flaws, all of its members have a welfare state.
I was speaking specifically about the United States in that post.
If the US were to open its borders to the world we would likely see a flood of low skilled immigrants. However the counties in the european single market have relatively equal economic opportunity, so you don't see floods of people immigrating from one single market county to another.