It has been known for years that immigrants are net contributors to the British welfare system. (For example http://www.economist.com/news/britain/21631076-rather-lot-ac..., and elsewhere too.) What's the point of repeating that old trope? It won't become any truer if more people say it.
That may be true in the present, but I think people are mainly concerned about the future. I strongly believe in a basic income, but implementing it in a country with open borders would be impossible. Same problem with the US, where no individual state can implement socialized health care, or they would be swarmed with sick people from every other state.
As for voters in the UK, I think they are concerned about future immigrants, not the current immigrant population.
That third option isn't as viable as you might think -- it leads to a dissatisfied, cohesive underclass that likes to agitate for big change, often returning to the "freebies for everyone" option.
So which is better? Providing a social safety net for "everyone" where "everyone" is defined as "only citizens of this country," or allowing a much larger "everyone" (people from many or all countries) to move to whichever place they deem to have the greatest opportunities?
I currently favor models that go after "easy exit, hard entry". Freedom of movement without standards causes problems. We should be free to go where we please, but it's up to other nations to set the price.
Within a nation, tiered citizen privileges with some sane defaults should control the degree of social security. Keep human rights intact, keep a basic standard of living intact, but ensure that all work is productive and that the people receiving welfare have a plan to not be economic deadweight.
I'm just one miller on the content farm: if there's one thing that I'm going to take away from this, it's that my ratiocinations don't mean jack shit. I'm still curious as to what other people think.
It would deter immigrants who are coming for economic reasons and don't make it or are just coming for the benefits to begin with. There of course also should still be a pass to citizenship.
The social safety net is not he opportunity that I want immigrants to be looking for and I say that as a immigrant myself. If I had come to the US and ended up unemployed soon after my arrival, the US shouldn't have had to pay for me. If I don't like that, I can always go back where I came from. Of course it's easy for me to say since I would be going back to a wealthy European country with comfortable safety net and to middle class parents.