I'm starting a new thread here because the topic splits from rebirth.
As far as I can tell, where humans differ is in our ability to have abstract thought. Meta-thought. We think about thinking. We evaluate our beliefs. We rationalize. We reason. We philosophize. We justify. We argue. We attempt to convince others and ourselves, not just to modify behavior, but also purely to modify thought. We grandstand and make wild assertions on internet forums. We become dissatisfied or satisfied, purely on a meta-thought level. And of course, we create amazingly complex ideas about our own existence which are rooted in and perpetuate the confirmation bias that we are superior, because much of our life is driven by an autonomic nervous system and brain that physiologically reward behaviors and thoughts that decrease any sense of temporary or long-term insecurity- because insecurity and fear can always be peeled away to reveal an instinctive drive to stay alive long enough to reproduce. (in my opinion)
So, for now, I believe that dukkha is caused by our capacity for "meta-thought," which, thankfully, is also what gives us the ability to think and act in ways that reduce or eliminate it. As far as I can tell, the Buddha's teachings all lead back to ending suffering/stress/dissatisfaction, and he expressed as much. As such, any pragmatic hierarchy of sentient lifeforms into which rebirth would be more or less desirable would be the exact opposite of what is conventionally accepted.
I've never heard, read, or experienced anything that has convinced me that anyone's experiences during, or resulting from, their dharma-practice contradicts the above expressed opinions. But I promise that I am completely open to any dialogue about it.
Having read through this again I think you are saying something more interesting and complex than animals and rebirth. I think I misread it as being about the emotional effects of Buddhist practice rather than getting at human beings over estimation of our reasoning ability.
There is a lot of work about how poor our ability to make rational choices actually is. Daniel Kahneman, Thinking, Fast and Slow, Daniel Ariely, Predictably Irrational, Kevin Simler and Robin Hansen, The Elephant in the Brain, Jonathan Haidt, The Righteous Mind, and I'm sure others.
Basically, human beings reasoning is largely post hoc rationalization, lipstick on a pig.
Others, like Joshua Greene, don't think it's quite so simple and binary. I tend to agree with this and think there is a Buddhist model that speaks to this view.
The kleshas of greed, hatred and ignorance are usually seen in much the same way as our unconscious biases and impulses. They are largely in control of our attitudes and behaviors, and our wild monkey mind (rational mind) is scattered and unable to exert proper control. If we can tame our monkey mind at least a little we can start to use it to slowly alter our unconscious attitudes. For example we can direct it to engage in metta practices which over time make changes to our base emotional state. So that our post hoc rationalizations now rationalize helpful, kind impulses rather than selfish, harmful ones. It's not so much that we become supreme masters of rationality, though that can be improved too, but that our unconscious attitudes have been improved via effective use of our feeble reasoning ability.
So our rational mind maybe lipstick on a pig, but wearing that lipstick can get us past the bouncer into the human ball.