There’s a couple different ways to look at this.
First and foremost, your vote is your right, and it’s an expression that is protected by the First Amendment as readily as it’s defended by the Constitution itself. Don’t let anyone tell you that you can’t vote for Gary Johnson. That includes anyone saying “I could vote for myself or a potato” yeah you could, but that would be stupid, because no one else is voting for you or a potato. Voting for a third party candidate because you believe that person is the best for the job is 100% valid as a choice.
Another way to look at it (which doesn’t invalidate the part where your vote is your right) is recognizing all of the other players in the game of the election process. Folks disregard Johnson and Jill Stein as candidates because they aren’t buying up gobs of ad time, and when the media DOES give them free publicity by covering them, it’s usually to ridicule them in some manner that deflates their candidacy (Johnson’s ignorance re: Aleppo and Stein’s desire to make Trump president in order to teach the electorate a lesson are singular examples). And the chief reason that the media at large (on both left and right) seems interested in doing this is because the electorate wants a Red vs. Blue race. By and large, third party candidates lack support and lack an installed base to draw from because of how entrenched the Democrats and the GOP have been for the last 40+ years.
The two-party system is a self-perpetuating engine, because rising politicians entrench themselves within the coalition that stands the greater chance of getting them elected, and the media continues to prop up Red vs. Blue because it’s a story that reads far easier to an audience that really isn’t interested in nuance. Most candidates who claim they want to upend that system get written off by the media (unless they’re able to seduce the media like Trump and Ross Perot were able to do) and consequently don’t get elected because they never find their base (because the media obscures it), so the system perpetuates itself.
So after saying all this, I’m not going to say that voting for Johnson is useless. It’s not useless. You think he’s the right guy for the job, or you think he’s a better option vs Trump or Clinton, or you’re protesting the two-party system that you feel isn’t representing you as a citizen. Your empowerment to do that is important, and you should always vote and always vote your conscience.
The media, however, is only going to pay attention to votes for Clinton and Trump, because they want the World Series of politics for an audience that’s hungry for an entertaining show, not an audience that’s actively engaged in the nation’s actual political character. And that’s something that’s ultimately solved only by a real revolution of thought, where the media recognizes that the game can be made more complex because the audience is in fact capable of understanding more than two opposing teams.
Takeaways: vote with a clear conscience. It’s a right that people lived and died to provide to us as citizens of this country, so it’s our responsibility to follow that spirit properly. But to affect change in the oligarchical structures that have perverted that spirit into a sideshow in the name of ad revenue and engagement numbers instead of actual engagement, it’s going to take a lot more than a vote. It’s going to take a movement.