This is not even an issue and I can't believe it's been brought up. Innocent until proven guilty is what you should consider.
If people wish to lurk, then there is nothing wrong with that - dont label people suspicious. They certainly wouldn't be kicked or banned from chat for doing so - that's absurd and very unwelcoming. We had many lurkers on IRC.
It's not hurting anyone and the people are chat have zero obligation to contribute to whatever discussion is going on.