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.
Whether this is true or not, it doesn't excuse ridiculous ballot access laws and the partisan ways that they're enforced. If you're not aware of the shenanigans that occur in this area, scan some past issues of Ballot Access News at
www.ballot-access.org. In brief, the duopoly often enjoy special status and give each other a pass on rules violations but hold third parties strictly to account or worse.