There's no anti-Nader conspiracy, but there's definitely an anti-third-party conspiracy. The ballot access requirements in many states primarily serve to perpetuate a two-party duopoly.
If the laws that apply to the private sector applied to politics, the DNC and RNC would be shut down on anti-trust and RICO grounds, and the principals would be headed off to prison.
Not comperable. In a plurality winner takes all voting system, and with our electoral college system, more than 2 parties just don't work very well.