That's the type of comment people make when they don't want to understand what the others side's actual views are, so instead they tell themselves a simple story they can believe rather than engage with the actual reason.
Both sides do it, but that's a prime example of one of the popular ones from one side.
It's Occam's Razor. In particular, nothing else explains why immigration became such a major issue for left-leaning parties around the western world only in the last 15 years: https://www.npr.org/2019/02/19/694804917/democrats-used-to-t.... As it became apparent that immigrants were a deep well of votes for people who wanted to expand the welfare state, immigration--which the left traditionally had viewed through the lens of economics and labor markets--became reframed as a civil rights and moral issue.
Both sides do it, but that's a prime example of one of the popular ones from one side.