But the idea of opposites is an interesting one. When are things opposite in nature, and when do our minds and language make them so?
The species, genus idea is an interesting one. It's also more a question of relationships and genealogies, rather than identities.
A word like "socialism" has many different definitions. In early 20th century Europe, it was a positive term. Even conservatives appealed to the "true" socialist idea. The debate here is as much about semantics as anything else.
You are a "splitter," who wants to use the word in a narrow sense. Others are "lumpers" who employ it in a more general sense. It's an argument that can't be won because it's about definitions -- axioms, rather than proofs or theorums or conjectures.
When someone says that the Incas or the ancient Egyptians were socialists, I balk. There ought to be a better word to convey similarities between the socialists of the last two centuries and ancient tyrannies.
But when someone argues that socialists are and must be democratic or egalitarian or anti-racist, I likewise disagree. This isn't based on an investigation of what self-identified socialists have actually said historically, but on present-day definitions. There have been racist and inegalitarian socialists.
In any event, Swedish Social Democrats left the control of the means of production in the hands of capitalist elites, yet they are reckoned as being on the left.