Open borders is the principle of free movement. It refers to the ability of people from any country to live and work wherever they wish, and its main function is to increase the pool of labour available for increased economic production. Advocates for open borders say that this would double world GDP, and that restrictions on movement constitute an unethical state incursion on the ability of individuals to associate freely based upon voluntary contracts. Critics of open borders argue that increasing the labour pool reduces the bargaining power of the working class, or that cultural differences will make the immigrants too dangerous or lazy to make the economic benefits worthwhile.
In my opinion, free movement is the most important human right. When individuals are given the widest possible horizon of people who they may associate with, the boundaries of human creativity are expanded. Free movement of labour is an essential component of the market, and the existence of multiple cultures within a society reduces the capacity for any one corporate entity to gain a foothold and consolidate its power into a monopoly.
