You are right, it cannot be ruled out. But something with such a defniitely effect should be pretty easy to justify. Find a telepath and let them tell me what I (or any test subject) is thinking. Has yet to be done under laboratory (or any verifiable) conditions, whereas quantum mechanics have. Until telepathy has verfiable and reproduceable results, or a shown scientific basis then I regard it as much a mythical item as is much of the Bible.
The Scientific Method is an axiom, something taken as true without proof. It has been so successful in our search for knowledge that its universal applicability is taken for granted even though we cannot prove this is the case.
A key factor in this axiom is the notion of the independent observer, that the phenomenon can be measured without affecting the outcome.
Surprisingly this notion persists despite the well known situation in Quantum Mechanics where the act of observation is integral to the value of result.
Quantum Mechanics overcame this problem by working in terms of probabilities.
Quantum probabilities allow for an event that would be considered impossible by classical standards. Quantum Tunnelling is an excellent example.
Likewise telepathy should be impossible according to Classical theory because there is no known mechanism by which such information could be transferred. However like Quantum Tunnelling, it cannot be ruled out on that basis.
The postulate that telepathy aught to be easily demonstrated fails beause the act of external observation could potentially obstruct the effect.
Moreover the emanations from the sceptical observers could easily overwhelm any weak Quantum-like effects occurring between the subjects of the experiment.
In any potential telepathic experiment we do not even know the boundaries of the phenomon we are trying to avoid becoming involved with.