Honestly, I agree with you on this; however, the grandparent didn't say "Democratic or Republican politicians," which is very much the source of the problem you describe. Their wording was "conservatives or the left", which I think it is fair to say includes the people who identify with those political orientations—and I think you'd have a hard time seriously arguing that "the left" in America, to the extent that it even exists, is not strongly in favor of labour unions and worker protections.