I too would back a system of points.
We are libertarians, not anarchists. I personally believe the state has a role to ensure some degree of equality of oppertunity, insofar as a society where only the rich can be educated is not free, no matter how much government influence there is. This needs to be paid out of tax - this is unfortunate, but of course necessary, to ensure a free, meritocratic society. This means we have a state and a society - even if it's made up only of different inidividuals - that is open to abuse if it's allowed to occur. As such, we do need some checks on immigration.
And what better factor to allow immigration than on the basis of market forces? That way, if a person's deemed useful to the market, they can come in, and those who are not cannot. This has the effect of, for the most part, meaning that most of the immigrants who come will be able to pay into the tax system and thus not get a free ride.
I don't advocate total equality of oppertunity - that would mean stripping all resources from people every generation. I merely advocate a society where anyone can succeed in a meritocratic way if they are good enough. This has knock on factors for immigration.