Rationality isn't killed, psychedelics cause neurogenesis but not in the purely rational parts of the brain, so the "weight" of your rational thinking is displaced by new neural pathways. It's good for problem solving in that it helps abstract thinking but do it too much and you become spacey because too much of your brain is under developed and focused on abstractions. A few good trips are probably good for a person especially when they plateau or get stuck in life. But a hobby of it is a terrible idea that will see your rational mind totally displaced.