Psychologists absolutely argue that they should be included in STEM.

Social science is a science. That's the S in STEM.

> Social science is a science

Wake me up when social science can reproduce their studies and I'll consider it a science. Until then, I consider it akin to "humours".

Popperism is not, and has never been, the definition of science. Science is straightforwardly defined: it is a pursuit of research whose primary mechanism for gathering knowledge about the world is the scientific method. Difficulties in methodology aside, social sciences primarily use the scientific method, and thus they are science.

Yes, people call it science. Is it reliable? No. Therefore it's mostly irrelevant and at most it's an aid for strategy not tactics.