The arguments for the moral case for #openborders can be designated into three ideological categories, arguments from the libertarian perspective, arguments from the left and faith based arguments.
Joseph Carens- The Ethics of Immigration
Utilitarianism is the general idea that our goal should be to maximize total utility. It is related to the idea of cost-benefit analysis.
The arguments for the practical case can be broken down into four categories; (1.) benefits to migrants (2.) benefits to immigrant-sending countries (3.) benefits to immigrant-receiving countries and (4.) global benefits.
Given the huge worldwide demand for migration from underdeveloped countries to the developed countries, particularly the United States, a prima facie case can be made that migration probably benefits the migrants a lot. The case can be made in two ways:
Free migration creates a number of benefits for the people who choose to remain in countries that are net sources of migrants
There are many harms to immigrant-receiving countries that various critics of immigration have pointed out. It is not axiomatically true that the benefits to immigrant-receiving countries outweigh the harms.
#Openborders are expected to yield a number of global benefits. The majority of the benefits accrue to the migrants themselves, while some accrue to immigrant-receiving countries and immigrant-sending countries.