What "heretical" ideas are there in science - such as the quantum brain, cryonics, the denial of global warming, which are not clearly recognized as pseudoscientific, but not desirable?

Aliens are the same.

Why no one remembered aliens?

The most classic example, I think. No one denies the possibility, but everyone rolls their eyes)))

From an area close to me - the theory of "fixism", which rejects the movement of continents and insists that the main role in the formation of the relief is played by vertical movements in the mantle. Back in the seventies it was (at least in Soviet geology) mainstream, now it belongs to the category of unmentioned in a decent society.

Ether theory, for example. I mean, of course, not an alcoholic compound, but a hypothetical all-pervading medium, the vibrations of which manifest themselves as electromagnetic waves. It was proposed by Descartes in the 17th century, then based on the works of Maxwell in the 19th century, it was substantiated. However, at the end of the same 19th century, scientists faced various difficulties and were forced to admit that the electromagnetic field exists by itself.

Recently, it is clearly not desirable in the scientific community. For example, a strange old man was hanging around in front of my university, trying to sell his book on the theory of ether to the fledgling minds of students. And my physics teacher also denied this theory, but argued that it would greatly simplify the understanding of physics, as well as the solution of many problems.

I am very wary of the theory of "global warming" for many reasons, which are quite long to explain here.

In addition to the above, there are many harmful and destructive quasi-scientific ideas and memes that circulate around the world, and some are very, very active. I will cite a couple of the most active and harmful ones.

1. The theory about the dangers of GMOs, that eating GMOs can cause an increased risk of cancer, brain damage, infertility, etc. There are even several very popular among followers of "scientific" works on this topic (by Seralini, Ermakova, etc.).

2. The theory of the dangers of vaccinations and vaccinations as such. There are also "scientific" publications on this topic.

3. HIV dissidence, or the theory that HIV is fiction and does not exist. (These I would generally forcibly isolate, although I am not cruel)