But for some reason, they were very resistent that they were sad simply because their brain produced a lot of the sad chemicals

And with good reason: brain processes aren't only about the amount of neurotransmitters; receptor sensitivity is key. That's how addiction works, after all, and why set amounts of drugs tend to become less effective over time. And, of course, the structures formed by the neurons are vitally important. Neurotransmitter emission and detection systems alone don't encode anything in particular, it's how they're wired together that gives them function.

If you must attribute a complex behavioral feature to fundamental biology, at least use a plausible attribution, not the nonsense that's meant to persuade.