Open borders cannot be dismissed as a utopian idea, argues Harald Bauder, because they do not propose an alternative way to organize human society but rather are a critique of closed or controlled borders.
Restrictions on mobility can only be justified if it can be shown that those restrictions prevent significant harm. Since research indicates that open borders will be better for both the natives and the migrants, and at the very least have not been shown to cause major harm, those restrictions are unjustified.
Free migration is the most effective way to reduce world poverty. Migrants from developing countries can earn higher wages after moving to a more developed country, usually lifting them from 'developing world poverty' to 'developed world poverty'. They also send remittances to relatives in their home country, the flow of remittances being estimated to be around three times the global foreign aid spending reported by the OECD.
A literature summary by economist Michael Clemens leads to an estimate that open borders would result in an increase of 67-147% in GWP (gross world product), with a median estimate of a doubling of world GDP.
From a human rights perspective, free migration may be seen to complement Article 13 of the Universal Declaration on Human Rights: (1) Everyone has the right to freedom of movement and residence within the borders of each state. (2) Everyone has the right to leave any country, including his own, and to return to his country.