Unions (at least in theory) have a way of bringing an employer to the negotiating table by getting a large enough portion of the employees to stop working and bring the employer's business to a halt. in the days of factory picket lines, they were able to prevent other people from working even if they wanted to. this is what gives a union negotiating power. I can't see anything similar for OS developers. What would be the threat? "We'll stop giving you free code?"
regarding a protection union, what you're talking about seems to be legal insurance, and that already exists, but it's significantly more expensive than $20/month.