You seem to have a really cynical outlook on all of this. I, too, am a scientist by profession, and I've always been a bit of a pessimist, but I think sometimes, it's worth giving people the benefit of the doubt.
It looks like you don't think your bariatric team has your best interests at heart. I know you've been burned before, and I also know what it's like to be constantly judged as stupid, lazy, noncompliant, untrustworthy, unworthy, etc. because of my weight, so I can understand your feelings about this, but don't forget that these are people who have devoted their careers to providing weight loss surgery. I'm not saying that they all genuinely care about alleviating the plight of the obese, or that they're sympathetic toward those of us in a position of needing this surgery, but I doubt there are very many medical professionals in the bariatric surgery field who are out to punish and criticize fat patients just for fun (or out of personal dislike of fat people). If for no other reason than their own self-interest, chances are that they want patients to succeed with weight loss surgery, and they are probably doing what they believe will contribute to their patients' success.
Another thing to keep in mind is that sometimes people can be right for the wrong reasons. I've run into this in my own job, where someone has told me something that didn't seem to make sense, and I (as someone like you with an inquisitive mind) have gone looking for the real story, only to find that what I was told was correct, even though the reasoning was not. In this case, your dietitian might be giving you good direction even if she doesn't actually understand what she's talking about. Just because that dietitian (or even the whole bariatric team) doesn't know or understand the reasoning behind the rules, it doesn't necessarily mean that the rules are incorrect or arbitrary.
Finally, if you hang around this forum for long enough, you will see that many patients want and need a lot of hand-holding. Some people would rather be given strict but arbitrary rules than loose guidelines. People are constantly on here posting questions like, "I had surgery X days ago; can I eat Y?" And honestly, considering that, I can't blame surgeons at all for wanting to make things as black and white as possible so they don't have to spend all their time answering these incredibly specific questions, tailored to each individual patient. Most patients are not medical researchers, and many want definitive instructions from their doctors. Many people would be paralyzed with indecision if they were told, "Some studies say X and others say Y; you figure it out."
Ultimately, it's up to you to decide how closely to follow your surgeon's directions, and if you do your own research and believe you have found a better way, you can make that decision. But I would venture to say that you will likely have a better experience if you have a mindset of working WITH your bariatric surgery team instead of taking an adversarial approach.