"Libertarianism is a moral and political philosophy that argues in favor of a strong presumption of letting people engage freely in mutually consensual activity and on minimizing coercion in society. In the modern political context, libertarians generally focus on government-enforced and government-facilitated coercion.

The right to migrate can be considered a corollary of the libertarian view that people should be free to do what they please (individually or collectively) unless it violates the rights of others.

Libertarians’ view of obligations to strangers has two core premises.

First, no obligations to strangers beyond respecting their rights.

Second, a very strong obligation to respect their rights.

Together, these premises argue in favor of not letting concerns about harms to fellow nationals be a justification for opposing free migration."

Read here for the historical roots of the argument for open borders in the libertarian movement: