“In other words something like the theory of phlogiston.”
She laughed. “Exactly.”
--Red Mars (Mars Trilogy Book 1), Kim Stanley Robinson
Phlogiston was supposed, by scientists in the 1600s, to be an element that was in anything that could burn. Burning, to scientists, was called dephlogistication. The scientists had it the exact opposite of correct: they assumed that when something burnt, the phlogiston was being removed from it and absorbed into the air; this was why, they felt, a fire in an enclosed container soon went out: the air was too full of phlogiston.
Nowadays, we know that the process which makes something burn involves pulling oxygen out of the air and putting it into the chemical reaction that causes burning. We're so smart!
What did in phlogiston as a theory was real science: experiments and noting physical reality. One of the first observations to challenge phlogiston was the fact that magnesium gains mass when it burns, which seemed to run against the idea that phlogiston was contained in magnesium, since it was supposed to be given off.
That fact didn't trouble the pro-phlogiston scientists at all: they instead proposed that perhaps phlogiston had negative mass. The concept of negative mass is not at all identical to the idea of dark matter: matter we cannot detect or interact with in any way, because obviously scientists in our enlightened times wouldn't do anything like just making something up to cover the fact that their theories are not working out. Just because modern day scientists rashly publicize controversial claims that in fact are not strong enough to hold up to examination to try to support a theory that was first proposed in 1933 and has not been critically re-examined is no reason to hold against current scientists the fact that they ignore papers which find a complete lack of evidence for dark matter. In the end, it's not even important whether dark matter makes up 80% of the universe, or 90% of the universe,or just 26.8% of the universe, the important thing is that dark matter definitely exists and is a real thing, unlike phlogiston.
Phlogiston. Ha ha those old timey people were such lame-o's.