There is no grassroots democracy in the Green Party without organization at the grassroots where members participate and become informed. Incentives in the structure should favor active membership in locals over at-large members who float into state and national conventions representing no one but themselves. One of the specific laws invalidated had to do with the maximum amount of dues that a state party could charge members of its state central committee. At the national level it's even plainer. A series of US Supreme Court decisions starting in 1972 have said that no government has any business trying to tell a national political party nominating convention how to run its affairs, whom to seat, etc.
Parties have First Amendment rights to run their own affairs.
No government has any authority to tell the Green Party it can't charge national dues. If that's what they mean, good-bye grassroots democracy. If that' s what they mean, good-bye grassroots democracy. The idea that the members of the national Green Party should be state parties rather than individual members strikes me as another triumph of the corporate mentality over a democratic one. Internal Revenue Code 527 corporations.