Lindsay is wrong, as many have already explained. I like the fact that he drew attention to the occult (specifically Gnostic) origins of socialism, but he wasn't the first, as that distinction belongs to Eric Voegelin. However, the rest of his commentary on society and political theory is rather lack-lustre.
Exhibit A:

Exhibit B:
The Liberal-to-Marxist Pipeline
Exhibit C:
On the Hatred of Humanity

There is nothing "reactionary" about socialism, it is a revolutionary ideology, and all the things that utopian socialists see as "mistakes" of scientific socialism are, in fact, their logical conclusions.
TLDR:
Communism didn’t “fail” in Cambodia, it succeeded, and the death toll shows that. They want to accelerate the process of the “end of history,” so they introduce the state police [sic](should be “secret police”), gulags, mass starvation; these things are part of the process, not a “mistake.” This is where I disagree with James Lindsay, who said these things were “mistakes,” but by reading someone like Stalin, their intent becomes obvious. - Lewis Barton