We would need a third party, like the government or a nonprofit. When a company or companies get large enough that they monopolize a niche, when they apply arbi

We would need a third party, like the government or a nonprofit. When a company or companies get large enough that they monopolize a niche, when they apply arbitrary restrictions, said restrictions can be challenged in court. If Uber prevents people from working from them who disagree with a certain party, people can sue them and argue that it isn't a justified restriction. Preventing people from working who don't pass a background check is justified, because it protects the safety of customers (assuming the background check doesn't unfairly weed out certain groups). Whatever restrictions are required / allowed / banned is up to society as a whole. Probably we would generally err on the side of allowing things, because we like freedom, but ban anything which most agree is illegal, immoral, or dangerous.