In philosophy, there's a concept called the "burden of proof", which basically says "a positive claim must be supported, a negative claim can be assumed". This is because, to simplify the formal logic quite a bit, it's logically inconsistent for everything to be true, but not inconsistent for everything to be false. Therefore, if the truth is unknown, it can be assumed to be nonexistent until further evidence arises.

In science, this burden of proof idea is called the null hypothesis: we assume nothing is true, and look for experimental evidence to "reject the null hypothesis" -- that is, we assume a positive claim is not true until we find evidence that it is. There's a fairly straightforward inductive syllogism for why that approach is the most reasonable, which I'll leave out here (unless you'd like me to outline it?) for brevity.

Therefore, Tarot, ghosts, an afterlife, psychics, etc. are all subject to the same burden of proof / null hypothesis rejection process as any other positive claims: until there's empirical, reproducible evidence supporting them, we must assume they are not true. And after centuries of asking for (and looking for) evidence, and even a long-standing million dollar prize for any that can be found, all we've ever had in that regard is... personal anecdotes and deeply-held beliefs. Neither of which constitute objective evidence, and neither of which manage to be consistently reproducible.

So the null hypothesis stands: they aren't real, and I genuinely invite anyone to find the evidence to reject that assumption, as long as the evidence they find is logically consistent, objective, and reproducible without confounding factors (i.e. if such evidence can only be reproduced while someone is on hallucinogenics, or while someone is in a house with a carbon monoxide leak, or while other factors could more plausibly explain the results, or...)

Many renowned scientists and researchers were also mystics. Mysticism is a personal, subjective framework for insight and self-improvement that doesn't have to follow the rules of the scientific method.

And the guy who discovered the first evidence of the Big Bang was a priest. But both facts are irrelevant. A thing is not more or less valid because of who believes it; the only thing that changes the validity of a claim is evidence about why the claim is (or isn't) true.

"Mysticism is a personal, subjective framework for insight and self-improvement that doesn't have to follow the rules of the scientific method."

Anything that makes claims about how the world works does, in fact, need to follow the scientific method. Why? Because it's a process that's literally designed to counteract the most common mistakes and biases that humans make in order to find the truth, and because so far, it's been the most accurate and effective method of predicting the future.

If you want self-improvement or mindfulness, that's fine and personal, but making claims about the nature of the universe isn't a personal opinion, it's a statement of fact about things external to yourself that is either true or false irrespective of your own experiences.

What about situations where a known affect is well documented, but the 'how' is unknown and not explained? We accept some of these as real, such as the use of many medications - we can see that they work or produce an affect, but don't know how.

I'm not saying that we should accept metaphysical claims as true, but our world does not strictly follow the null hypothesis either.

I think the null hypothesis and the burden of proof applies to a specific claim that "this is how it works". There are plenty of phenomena "officially" unexplained by science yet, and that's ok. But claiming that some cards have some magical meaning doesn't make sense.

True. Calling BS on magic is fine. But it could also be wrong to claim tarot is complete BS. It's possible the effects of a tarot reading are explainable by things like observation bias, the subject changing their behaviors due to the reading, or the reader using some sort of body language reading to influence their "interpretation" of the cards.

Let's be clear in our definitions here: when people say "Tarot is BS", they don't mean "it can never get the right result"; they mean "it doesn't get the right result through some mystical, spiritual, or divine knowledge as the practitioners of Tarot often claim it does". Additionally, if a Tarot practitioner does not make such claims, and instead points to any of the psychological explanations you mentioned, then the cards are no longer relevant to the practice anyway since they are not involved in the true mechanisms.

The claim "this medication produces this effect" is a separate claim from "this medication produces this effect via this process ". In those cases you mentioned, the first claim has enough evidence to reject the null hypothesis, and the second... well, if we don't know how it works, then we have yet to find such a claim that has rejected its null hypothesis.

For instance, aspirin works as a pain reliever. This has been shown with empirical evidence. However, if I said "aspirin relieves pain by infesting your blood with microscopic fairies who kiss your boo-boos from the inside out" -- that claim does not have enough evidence to reject the null hypothesis.