the main reason they are stupid, is that the persons who are most similar will get a split vote. if the green party runs, it spits the vote with dems. if a libertarians runs, it splits with republicans. often, the most popular segment could lose, simply because of a split vote. this split vote thing, is called a 'spoiler effect'. the founding fathers weren't thinking straight when they made our electoral system.
on a related note, our system sucks, cause it's 'plurality voting', even if a politician is unpopular, they can take the primary or general election by getting a plurality that's less than a majority. trump v clinton... both were unpopular, yet they were foisted on the stage by plurality voting
i can relate to wanting options in our elections by third, fourth parties are not the way to do it. research rank choice voting, or approval method voting. those systems fix the problems we have with our system.
plus we do have primaries where there is often lots of choice. it's fair and sensible to only have two candidates if others were fairly evaluated and processed in the election.
all those 'we need third party' advocates dont know what they're arguing. i liked that idea when i was younger, only cause i was stupid and ignorant. these third party advocates seem so low brow and low intelligence