Each individual vote is the best that one can do, given their limited knowledge, their prejudices, and their fears. I know people with PhDs who voted for Jill Stein, and nothing could persuade them that their vote was thrown away -- they revel in the purity of their choice.
Where "stupid" comes in is in the aggregate. The result of all these individual actions is collective stupidity. The looming climate disaster was barely mentioned in the campaigns. It is collective stupidity to elect climate-denying, corrupt fools at this moment in history, just as it is corporate stupidity to focus on quarter-to-quarter profits when the burning of fossil fuels threatens to literally end the ability of humans to live at all.
For a big chunk of my life, I was a libertarian. Which, I finally realized, was a devotion to a silly utopian ideal in which productive geniuses would lead the way with enlightened self-interest. Burning up the planet you live on is not enlightened self-interest. Neither is selling products that kill people. There is no time now for the playing out of strong-man, fascist fantasies, or any other utopian scheme that is based on hatred of those who hold one set of ideals against those who hold another. (Fighting over pie while you are in the oven). Hands at each others' throats, they fail to see that the hurricanes, tornadoes, wildfires, heat waves, droughts, and superstorms are indifferent to politics.
Only the greatest collaborative scientific and engineering effort will save the human species from the climate catastrophe. Everything else is a distraction. And yes, the word "stupid" applies, especially since we cannot wait ten or twenty years for the politics to swing round from fascist to liberal.
Bottom line: even "educated" people do stupid things, and when they do them en masse, we are collectively stupid.