These little critters spread diseases as the other commenter already stated. Also, they inject an anti coagulant into the bloodstream of their victim. So people have woken up in the morning covered in their own blood and had to get medical attention as they would not stop bleeding. Even though this is usually not life threatening, I would not really call them harmless

The anti coagulant you speak of is in their saliva, not unlike mosquitoes. And is a very small amount. Not that these creatures would ever try to feed off humans but if it did bleeding in excess wouldn't occur unless the person was a hemophiliac.

considering the fact that there´s veen a recent rabies outbreak in the Peruvian Amazon region due to these particular bats biting humans, I think you're on the money. Usually these bats don't go humans and their unusual behaviour has generally been credited to clearing of primary rainforest (for timber and oil exploration) and consequent depletion of their natural food sources. just a thought.

... these bats can be undirectly harmful, being a vector of rabies living in an endemic region.