Basically, because socialism fundamentally requires centralized control, and I don't trust centralized control. I fully expect corruption and greed to exist, and to gravitate toward power.

Socialism is not a political philosophy based on belief, but simply the epoch that must follow capitalism, as it’s the first step in really resolving the fundamental contradictions of the latter—done halfway by the capitalist state apparatus, which aims to reconcile class contradictions whilst preserving their originator, and so itself falls into contradiction; the increasing socialization of production coming along with development contradicts the private ownership of enterprise, even still imperialism lends to the centralization of production/distribution as a resolution of the fall of the rate of profit (and this rears its head also in the sphere of automation, where capitalist development requires greater and greater productivity for competition, and yet, the greater the reliance on automation (for extension of productivity beyond human potential), the lower the rate of profit becomes as surplus value/variable capital comes from human labor power—this contradiction is unique to capitalism as it holds exchange-value over use-value, and so the necessary outcome is the resurgence of use value as the dominant force with a mode of production which serves the whole working populace rather than a few profiteers).

I don't trust society not to deliberately appoint a tyrannical megalomaniac: I've seen them do it entirely too often.

Wrt socialism? Do you understand how material conditions work? Which "societies" as a whole deliberately appointed tyrannical megalomaniacs? "Entirely too often" means you have to name at least five.