In the most fundamental aspect they are reactionary. Socialism and leftism more broadly are about the furthering development of mankind, the social progress of development.

Primitive Communism -> Tribalism -> Agricultural Society -> Feudalism -> Capitalism -> Socialism -> Communism

If you reject this advancement and want to regress backwards to primitive communism, that is, by definition, reactionary and backwards. Let alone all of the implications of this (mass genocide, 99% of the population dying, trans and disabled people dying or being severely disadvantaged, collapse of all development and movements towards a non-predatory society)

I would say anprims are anti-human or deeply dumb, and are more reactionary than fascists and monarchists even.