Whether or not you believe it's good or bad, we have a 2-party system here.
Why do you think Bernie is running as a Democrat and not an Independent?
When was the last time an outsider (not RNC or DNC) won a race for high office?
Whether it's Green, Libertarian, Democratic Socialist or Independent, no third party will ever have the votes to beat all candidates on a ballot with and (R) or (D) by their names.
It's naive to believe our system will change soon. Unless someone more popular than Trump, richer than Bloomberg, and more charismatic than George Clooney runs as a 3rd party candidate, it's unlikely the masses will break from their habit of voting for a Dem or GOP candidate.
More and more people are labeling themselves as Independent, but that's to avoid having to choose either of the corrupt big two. In the voting booth, however, they will on average tend to vote as they always have.