They aren't completely equivalent, though it's pretty close, sadly.

I agree that it's better for someone to get involved with a third party, but if that third party's electoral strategy is to simply try and receive more votes, then they're actively hurting under the US' terrible voting system. (This is under the assumption that this third party is less right wing that the Democrats, and that you don't want the Republicans to win).

Any third party that is actively campaigning on getting preferential voting across the line by influencing the Democrats from the outside (yeah, first part the post is that terrible that this is necessary), or is revolutionary in nature, is okay in my books.

The rest are doing active harm because of the spoiler effect.

"Blue no matter who" is really, really dumb, and people really ought to get involved with groups within and without the Democrats to vigorously push for electoral reform, and better yet the abolition of capitalism and implementation of actual democracy (the US can barely be considered a democracy).

Parties that just are campaigning on: 'Hey! Vote for us because we're better' with no actual strategy of changing the system are dumb, also.