The most obvious problem is probably that it's way easier to develop bots/cheats for those games.

Since I'm currently developing a WebGL game I'm actively searching for ideas to detect that behavior.

The only solution I can think of is, to capture any data with timestamp coming from the client and applying some tests to it like "is the client sending more messages than a normal client" or more advanced: sending the input through a statistical filter to detect possible cheating and investigate from there on.