That's not what "no borders" mean. Of course local communities have right to self-determination and thus also who gets to live in them.
It doesn't. It implies judging them based on their individual merits and values.
What? Yes that's a part of it.
In the end, it's about abolishing the need to even have to have people work and thus making individual merit irrelevant, but until then it matters a lot.
I am an anarchist, but I'll quote Marx:
"one man is superior to another physically, or mentally, and supplies more labor in the same time, or can labor for a longer time; and labor, to serve as a measure, must be defined by its duration or intensity, otherwise it ceases to be a standard of measurement. This equal right is an unequal right for unequal labor. It recognizes no class differences, because everyone is only a worker like everyone else; but it tacitly recognizes unequal individual endowment, and thus productive capacity, as a natural muh privilege. It is, therefore, a right of inequality, in its content, like every right. Right, by its very nature, can consist only in the application of an equal standard; but unequal individuals (and they would not be different individuals if they were not unequal) are measurable only by an equal standard insofar as they are brought under an equal point of view, are taken from one definite side only – for instance, in the present case, are regarded only as workers and nothing more is seen in them, everything else being ignored. Further, one worker is married, another is not; one has more children than another, and so on and so forth. Thus, with an equal performance of labor, and hence an equal in the social consumption fund, one will in fact receive more than another, one will be richer than another, and so on. To avoid all these defects, right, instead of being equal, would have to be unequal.
But these defects are inevitable in the first phase of communist society as it is when it has just emerged after prolonged birth pangs from capitalist society. Right can never be higher than the economic structure of society and its cultural development conditioned thereby"
That's not what "from each according to ability, to each according to need" means.
Again, the whole point is for the self-determination of local communes.
In many cases, letting people starve at our walls is a pretty bad idea as it spreads unrest and violence that might impact us gravely and it is thus against our self-interest.
That is of course beyond the ethical rammifications of the "fuck you, got mine" mentality.