Actually there is something wrong with the concept of families - it's unfair that some children do not get the same level of love and attention (and dentist visits) you provide for your children. However, families are not obsolete because there's no obvious solution to the problem of unfairness between families, and given human nature perhaps there will never be a solution.

But outside the family there is a solution: Just treat everyone equally. There's no biological reason why I should care about the passport of a man I have never met, any more than I should care about his race or tribe or religion.

Yes, mass immigration would mean that you would be worse off and the immigrants better off (although spreading the immigration period over say 50 years might limit your costs in this equation). But isn't that the right thing to do? Do those people deserve to live in absolute poverty? If not, doesn't that mean you have an obligation to help?

Nationality is not yet an obsolete concept, but society is slowly moving in that direction. I think Charles Darwin said it best:

"As man advances in civilisation, and small tribes are united into larger communities, the simplest reason would tell each individual that he ought to extend his social instincts and sympathies to all the members of the same nation, though personally unknown to him. This point being once reached, there is only an artificial barrier to prevent his sympathies extending to the men of all nations and races."