I don’t believe anyone in this thread has demanded an unlimited amount of proof that will never be enough. Can you please point to a real example?
Demanding an unlimited amount of proof that will never be enough, or “endless proof,” is not the same thing as requiring randomized, placebo-controlled trials with treatments randomly assigned. You can’t know if a specific treatment is effective if you don’t control for bias in the experiment, and if there aren’t enough subjects in the trial to do a statistical analysis that will tell you if the treatment is effective. You also need to replicate the results (do more than one experiment). In the case of testing vitamin supplements, it is possible to administer a placebo, and to have treatment and placebo groups randomly assigned, and assigned in a blind fashion. It is also possible to analyze the results in a blind fashion.
Pointing out the fact that a study was not done with the above features for limiting bias, or had bias possibly introduced for another reason, or was not followed by a statistical analysis, or did not have enough subjects to do a valid statistical analysis, is not in any way the same as saying a study is invalid because the author beats his wife or hates cats. The former criticisms have to do with whether the study shows us any real benefit from the product tested. The latter criticisms have nothing to do with the study or the product at all.
If a study has serious flaws in the data collection, or the methods used in the study, or anything else that might introduce bias in the results, that is very relevant to anyone seriously interested in knowing if the product tested really works. If a study is seriously flawed in a way that can introduce serious bias, it doesn’t tell you anything about whether the product is effective. You can ignore those flaws if you wish, but it isn’t nit-picking, or the same thing as demanding “endless proof,” or the same thing as demanding “an unlimited amount of proof that will never be enough.”
On the other hand, if you just want to buy and use a product and don’t really care about whether there is any reliable evidence that it works, or evidence that it might have risks you should know about, then why make the effort, or pretend to make the effort, to look at any studies or reports at all?
Your information about patents and products containing vitamins, by the way, is not accurate. You can obtain a patent for products containing vitamins and other products containing naturally-occurring ingredients. A federal appeals court in the US issued another decision in the last few years affirming this. But if you want to advertise such a product as being effective for a health condition or disease, you have to have adequate substantiation for your claims, as spelled out clearly in guidelines available free of charge from the FTC and FDA.