When a theory has stood up to repeated experimentation, it will simply not be disproven. A better theory might be devised that explains that experiment and more, but the experimental result is not going to go away, and the theory that has stood up to such experimentation will not disappear. At least, that's the way it is in physics.
Note that I never said "conventional wisdom" is never overturned. I said well-established theories are never overturned in their area of validity. A well-established theory is not mere "conventional wisdom".
In the case of ulcers, you're not talking about a well-established theory supported by repeated experimentation. In other words, it was not the case that hundreds of experiments showed that ulcers were not caused by bacteria, only to be upended by one experiment that showed they were. (That being said, I am always skeptical of results in medicine. Things get very difficult when you start studying humans; it also becomes almost impossible to ensure that the scientist's personal biases don't affect the results. Moreover, the news media like to tout every tiny study, regardless of how statistically insignificant it may be, as the final word on that topic; they love to create the impression that something groundbreaking has happened.)
Your statements about the scientific method are not correct. If you're a physicist and start arguing that a well-established result be re-tested, you will simply not be taken seriously, unless there is something novel or challenging about the experimental method you're proposing, in which case it is really the method being tested rather than the theory. If established results were, as you claim, "up for peer review and debate", science could never advance. We would still be debating things that were established centuries ago.
There is a reason almost all climate scientists believe climate change is real. You can argue about the meaning of the word "proof", but it is extremely unlikely that the entire community of climate scientists are wrong about their interpretation of the data. That is hard to accept, considering what the consequences are likely to be, but all that means is that our human biases are pushing us very hard to believe that there must be something someone is missing. That's just wishful thinking.
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