Milton Friedman was largely in favour of freedom of movement, but he famously noted that you can have either a welfare state or open borders - but not both. (And note also that in a broad interpretation, things paid out of tax money and given away for free, like public highways, public schooling, etc., can also count as part of a "welfare state".)

The main difference between goods/services and people is that goods don't have rights, but people do. So if people are obligated to pay for the 'positive rights' of people - the "right to food", "right to shelter", and so on, then migration imposes genuine costs. (Of course, this is different from 'negative rights' - the "right to free speech", the "right to freedom of association", and so on.)

Interesting, thanks

Libertarians do make exactly that argument about immigration. And people who disagree make exactly the same counter-argument - that even if it is a net benefit globally, some people might not like the result locally.