Definitely heard this sort of view given by other people (including on here before), and I do understand it. However one of the main issues with that from my POV is that getting to achieving one international working class will take a long time. Scotland (or other similar countries) becoming independent in the meantime has the potential to improve lives in that country in the present day.
And then with something like Brexit, Scotland as a whole voted to remain part of a larger group. by being so tied into the UK though the agency to make that choice was lost, so the hope is that by being independent there would actually be more ability to engage in worldwide international spaces without your positions being held back by a Government that doesn’t “truly” represent your people.
Very rough and ready, and lots of assumptions and positive spin on that, but that’s at least some of the concepts involved.