Is Many Eyes a Fallacy?

Crowdsourcers often repeats this idea that because so many people are looking at something that it is less likely to get bad stuff through. While this can follow rationally, we have issues like Kitty Genovese which indicate the opposite is true, the more eyes on the issue the less likely people are to speak up.

There is really no error in reasoning here; perhaps just a failure to understanding human behavior. There is truth to the crowdsourcing effect; also referred to as wisdom of the crowds. There is also a concept in psychology known as the bystander effect, which explains the Genovese case you mention (although do have a read here to get an update on what we know about this case: https://en.wikipedia.org/wiki/Murder_of_Kitty_Genovese#Accuracy_of_original_reports ). These are two different effects. The crowdsourcing effect is about knowledge and the bystander effect is about responsibility. With the former, people are more aware of their role to contribute where with the latter, there are no roles—it is about someone stepping up, usually at a personal risk.

There are many nuances with both of these effects that are situation independent. Perhaps errors in reasoning can be found in specific examples, but generally there are no fallacies here.

As Dr Bo said, there's no error in  logic  here - however, the premise is debatable due to various cognitive biases and the like. It depends on the type of people whose eyes are on a thing, and what their priors are.