Nader in 2000 (as well as Perot in 1992, although people seem to forget that one) showed that under our current electoral system, promoting third parties can lead to the election of opposing candidates that you might have defeated otherwise. Pretty much the only relatively safe mechanism for marginalized voters to express their disapproval is with primary challenges.
Nader made no effort to run in the Democratic Primary did he? He denounced the party elite from the get go and hoped to get people to back him. - Seriously magical/wishful thinking.
And look, that is what Sanders is doing.
If Sanders loses the primary, then we get Hillary in the general, my second choice based on the current crop of all candidates. If Sanders wins the primary, then I get first first choice running in the general.
You say that Sanders can't win the general and you are willing to settle right now because of that, and that is your right. I think that you, and a lot of other people, are really underestimating him, especially when compared to the who he might be running against in the general. Sanders vs Trump? I mean, come on!
I have no objection to Sanders running, I have no objection to people voting for him if they think he represents their values.
I have come to the conclusion that unless we see a more definitive movement, which a major shift in Congressional elections would be evidence of in my opinion, that Sanders is not a viable 3rd party candidate.
I lived through 2 movements, the Vietnam War protests and the Civil Rights movement. Maybe because I'm comparing what we are seeing now with Sanders, to what it took to effect the major changes in the Civil Rights movement and the Vietnam War protests. What I see is that the Sanders' movement is too weak to successfully change the country. To me it's obvious.
It's a much stronger effort than Nader's, of course. It has more substance than either Trump or Ross Perot claiming a magical business leader can fix everything. Trump and Perot has/had a fair following of people convinced the private market can run the public sphere more effectively than the public can.
Sanders has a following. They are passionate. Sanders doesn't have the country behind him and at this point in history, he won't.
Time will demonstrate that. I'll keep an open mind, so should Sanders' followers because when it pans out either way, we need to be able to accept the outcome, and not keep believing in the thing that is clearly not happening.
If Clinton stays up in the polls and starts winning state primaries are you going to blame people who had no faith the 'movement' was actually there, like a self-fulfilling prophesy?