Well that's a bizarre way of going about making your point. First of all, workers had plenty of choice, and moved around frequently. Secondly, it wasn't the lack of choice, but the fact that those choices were universally bad, that made labour unions necessary. Thirdly, there is arguably less labour mobility now than there was in the 19th Century, so if it was a matter of less choice = more unionisation then you would expect labour unions to thrive nowadays. You've gone this circuitous route of shoe-horning "labour mobility" or "options" or "little choice" into your narrative, when in fact you can leave all those things out and just say that poor working conditions in the 19th Century made labour unions necessary, whereas massively improved working conditions today makes them much, much less important. This is something that I would broadly agree with, and that most people would agree with, barring Traitorfish and a lot of the other communists. Shoe-horning anything to do with labour mobility or lack of choice or competition into it does nothing to help your argument and only opens you up to accusations that you are fetishising and idealising "competition" (as you libertarians are wont to do) and allows the history nerds on this forum (who get a hard-on for historical inaccuracies) to play this game of historywang.