To the extent that voters cast for a third party candidate in protest, I agree with you. However, to the extent that voters cast for third party candidates because that's whom they truly wanted to see in the WH, I don't agree with you, and I don't for two reasons:
voting for third party candidates is always a waste of a vote.
what we need to do is chuck the electoral college and have a system like the French have. The top two vote getters go into a runoff if no one gets 50%.
There's no question that in each of the "battleground" states that Trump won, third party candidates won more than enough votes to have given Clinton the win had those votes gone to her. AFAIK, Johnson won the largest plurality of third party votes; however, what share of Johnson voters were choosing between Johnson and Trump vs. between Johnson and Clinton is not at all known to me. The fact that Libertarians are generally part of the conservative bloc of voters suggests they were making the former evaluation. That Trump is such a despicable human being suggests their analysis was of the latter nature.
Well, that's an easy one to figure out.
Trump got about the same amount of votes as Mitt Romney and John McCain got. Between 45% and 47%, between 60 and 63 million votes. Trump didn't move the needle on that end of the spectrum, which is why I think guys like Mac who sit here and whine that we aren't hugging the Nazis enough and understanding their White Trash plight are truly silly.
Spoiler alert. The White Trash is in a "plight" because for the last 40 years, they keep voting for Republicans who screw them over to help the rich. That's why they have a plight.
Now, Hillary did move the needle- downward. She got about the same amount of votes as Obama got in 2012, but it was only 48% of the electorate.
Meanwhile, Gary Johnson went from 1,275,951 in 2012 to 4,489,233 in 2016. He more than tripled his vote total. Now, if Hillary went down and Trump stayed flat, where do you think those votes came from?
It wasn't from the Republican Base that Neville Mac thinks we just need to appease some more by sending just some brown people home. No, it was from the far left who voted for Stein, or the moderates who voted for Obama last time, but just didn't like Hillary, but since she was going to win anyway, why not do a protest vote?
Now, final note. The biggest problem at the end of the day was Mrs. Clinton herself. She isn't likable, she always comes off as a little phony. And you can't discount good old fashioned misogyny. Go to a Star Wars forum and see how much people are freaking out about female leads. But what she wasn't was "Far left winger regressive" like Mac goes on and on about. She made real appeals to the middle, often at the expense of the left.