It is out of a spirit of benevolence, actually. I do not like seeing people lose money due to being influenced to buy a stock based on poor, bad and even malicious information sources.
And yes, there is also a selfish reason for those that just cannot fathom an act of benevolence. And that is that the money that might be invested in a crap stock could instead go toward a much better play where many more people can all make some nice cash, including me.