Yes, it's worked out terribly for some people, but everyone I know who have done upwork jobs on the side have had next to zero problems.
I don't use them anymore, as I've gotten out of the tech industry and became a professional baker instead, but I get the feeling that we on HN tend to hear a few horror stories, and ignore the thousands of success stories.
I'm not saying that there shouldn't be changes made, but anecdotal evidence does not instantly justify a witchhunt and boycott.