Consider: If a force exists which is capable of being neutralized through the unconscious intent and will of observers who do not want to see it, then how do you measure it? I've never seen an experiment performed which takes this question into account.
Perhaps they could gather a group of observers all of whom genuinely wish to measure said "force" and take measurements while minimizing the "negative influence" of outsiders. While it would be difficult or impossible for any particular group to reproduce, at least it could be filmed and meticulously documented to determine if there were methodological faults.
Of course, that will never happen. Many believers don't care to have their cherished notions put to the test, and many skeptics would immediately dismiss such an experimental setup, but one who would thoroughly investigate such an experiment would be James Randi.
Your are correct in that he is not a scientist, but he is a rationalist. All he asks is for someone to actually demonstrate what they claim to be capable of doing in an experimental setup that removes opportunities for deception. Many have tried, and all have failed. All participants have to agree to a testing protocol beforehand, but it is not forced upon them. If people were truly capable of performing these feats, it should not matter whether or not a double-blind experimental setup is used. Unfortunately, such rigorous testing is needed because people have an amazing capacity to deceive, both themselves and others.
Personally, I am open to new ideas and experiences, but I ask that someone actually provide evidence. Since the beginning of recorded history, mankind has held one bogus notion after another. Our minds are pattern seeking devices, and they are quite capable of seeing patterns where none exist. Ideas that map usefully to reality are investigated, modified, corrected, and revised until they match the observable world as closely as possible.
Subjective experiences are just that, subjective. In meditation, you may experience vivid images, the feeling of other "presences", phantom noises, or other phenomena. However, wholly subjective experiences are by definition not demonstrable to others. Dreams, hallucinations, inner voices...they may have some deep meaning to you, but it is likely because they emanate from your mind, not the outside world.
Anyway, while science is by no means complete, we do have a handle on the basic forces of the universe. While there may be some untestable force only measurable by believers, it is quite unlikely. What is likely, and common, is the desire for believers in the paranormal to clock their beliefs in jargon to make them sound more scientific than they truly are. Using the word "force" doesn't make it science, only observation and experimentation. However, such a force would be a very useful device for charlatans to explain the failures of their abilities any time that they are put to the test.