>I imagine that if one would thoroughly internalize the belief that we're driven by purely rational, mechanistic forces, diving head-first into irrationality in an attempt to search for (or somehow invent) freedom and meaning, would be the only rational thing to do.

Nah. Compatibilist free will is entirely real, and meaning is more-or-less a built-in byproduct of living life. In fact, the most common reason people "lack meaning" is precisely because they're trying to be as "free" as possible by minimizing the attachments that make life meaningful.