Does SOMETHING really happen that is the basis for this? YES--the tipoff is the "alien" descriptions look ALIKE. If people made it up everybody would have a different description of the aliens, now wouldn't they. 50 people told to "invent an "alien" with pencil and paper would draw 50 different "aliens". So we can pretty well much assume that the witnesses DID see the same thing whatever it was (at least before 1977 when the popular alien became public after the CE3 movie)
Since we do NOT want to assume REAL aliens, then WHO is responsible for the events and why?----Obviously, such a LARGE scale hoax, because of its scope and expense could only have been done by some GOVERNMENT agency--Like NSA or CIA---but WHY? That's simple too, obviously they are examining people either because of a weapons accident (Nuclear, toxic or biological) or a disease, that would cause a scandal or panic if the news got out.---or it might just be an unethical weapons test experiment----Face it, an agency that would carry out something like the "Tuskegee experiment", would not be beyond something like this.
But what about the "Aliens"? It is an ingenious ruse to confuse the witnesses and make them less willing to talk, or render them unbelievable if they did. ---Should the normal amnesia drugs used, wear off. It's the flaw in the system that opens it up to logical analysis---They USED the SAME Alien "dummy" or "animatronic" figure to frighten the witnesses------This results in similar descriptions that confirm the abductions actually happened.-----even it they were not real "aliens". Had the agency been smarter, they would have used a different "dummy" each time---THEN when the people talked, no accounts would have matched, and all would have been chalked up to "Lies and Imagination"--------BUT people DID see the same thing and the Logic above thus follows. No real aliens needed---it's the Government at work, and since it is top- down LOGICAL, it also knocks out the "Conspiracy theory" too"---as Conspiracy theories are built Bottom -up.
Unless you want to actually believe in REAL aliens doing it.