Some free market economists believe that competition is the essence of a healthy economic system, and that any short-term negative impact on individual economic factors that is caused by free migration is more than justified by the prospects of long-term growth for the economy as a whole. Whilst not defending fully open borders, political philosopher Adam James Tebble argues that more open borders aid both the economic and institutional development of poorer migrant sending countries, contrary to proponents of "brain-drain" critiques of migration.