>On the one side some 'bad other' could be using an undefined device to attack only American people, only in foreign lands, and for uncertain reasons.

If someone were trying to sour US-Cuban relations, then it would make sense that only Americans in Cuba were targeted.

It seems highly unlikely that 21 diplomats with the same symptoms (plus those in China) were afflicted with an innocuous medical condition. None of the doctors who wrote letters of dissent physically examined the patients. Though the specific nature of the cause may be up for debate, I highly doubt there was no adversary here.