Sorry, real life is messy.
1 - Some replicable tests are a good idea
Some people see Aliens at Roswell when they are there at night and take drugs.
This is a replicable experiment - is it because they have taken drugs or because Aliens are sometimes there?
Generally (sadly) if you have a randomised double-blind controlled experement that controls for the likely deciding factors, you can decide whether or not it is more likely because people take drugs (happily you cannot be sure about the presence or absence of aliens)
2 - Some replicable tests are a bad idea
Do the really expensive cancer|baby-saving|altzhiemer etc drugs we use really help?
This is also replicable experiment
Give some people the drug and some a placebo.
Not too ethical even if you disclose that there might be a placebo
3 - Some things cannot be replicated
Was it right to have QE - did we have the right amount of QE
This is not replicable.
You dont get to re-run an economy for the last 6 years - all you can do is watch and measure and argue about causation afterwards.
In the scope of psychology, you get a mix of all 3 experiment types. All these questions are very good questions.
What troubles me is that there will be a growing tendency to not attempt to answer the hard ones.
1) Occam's razor already tells you it's the drugs. Unless aliens show up only when taking drugs, or we suddenly get super-alien-viewing-powers when using drugs, aliens could be there. That's (apart from being ridiculous) such a complicated model compared to the simple "your drugs give you hallucinations" model (which we even know is true) model that occam's razor can rule out the other ones.
2) Erm.. you know that this is EXACTLY how drugs are tested every day? Not unethical. Extremely common.
3) You could run a simulation.