William Bernstein in A Splendid Exchange argues that pro- and anti- immigration (and free trade) positions are taken not as fundamental philosophical positions

William Bernstein in A Splendid Exchange argues that pro- and anti- immigration (and free trade) positions are taken not as fundamental philosophical positions by the left or right wing but by the different trade factors as would be expected considering the results of free trade or movement of labour under the Stolper-Samuelson theorem. A simplifying example is that in a field and region that is labour intensive but having a scarcity of labour, labour agitates against immigration and free-trade. It's a fairly convincing argument, though it references a trade model that is somewhat simplistic.