They have to be, otherwise the vast welfare state system collapses. It's why the big European welfare states can't handle huge amounts of immigration very well. The greater the welfare state, the greater the influx of immigrants that you're likely to see wanting to get there. The only reason the US was able to absorb the massive immigration it did on a few occasions in its history, was due to the almost complete non-existence of a welfare state at the time, immigrants had to make it on their own at very limited additional cost to the state or tax system. If you deployed a full European style welfare state in the US, and then attempted that scale of immigration again, it would collapse the political system and economy.

Sweden has more immigrants per capita than the US. It doesn't seem to be collapsing.

This is an interesting line: do you have links and research which support it?