ITT: proto-communists

Not at all. Fascism (or some form of "Enlightened absolutism") is the logical conclusion of Enlightenment and liberalism, and socialism is the negation of contradictions that follow.

I fail to see how when fascism is barely any sort of coherent ideology at all.

Liberalism has no intention of holding itself to its own standards. Liberalism is itself a negation of "divine right" hierarchies, but it replaces birthrate with "merit", it does not abolish the hierachical structure itself, and has no intention of doing so.

Socialism doesn't negate the contradiction, it resolves it. What you are referring to is largely a contradiction between liberalism's philosophy and its material outcome.
Liberalism naturally descends into fascism. Socialism reaffirms liberal philosophy against the new conditions.

Somehow I don't think Locke and Rousseau went to all that trouble writing shit they didn't believe in.

Except negative liberty bites the dust.

It's not "liberal philosophy" that socialism reaffirm, it's the actual goals of the Enlightenment which liberal philosophy fails to meet. A mere separation of church and state is not sufficient, therefore you have state atheism, etc.

fascism is not "Enlightened", it is the very negation of enlightement, actually i'd argue it is what happens when the contradictions of capitalism make enlightement imposible under the current mode of production, socialism would be then the negation of the negation, arriving at a higher enlightenment

A liberal parties collaborated with fascism during its rise because…?

because as i told you capitalism makes enlightenment imposible under it, so the liberal has to choose between an enlightened world, or a capitalist world, he then proceds to choose the capitalist world, because he confuses the two and thinks capitalism eventually will restore enlightenment, he doesn't see the contradiction

Fascism explicitly rejects the enlightenment and everything it ever stood for, right down to rationalism. The other user's are right, socialism is the result of applying the ethics of liberalism to the realities of capitalism.