Serious question, not a shot.
When people Jailbreak their phone with something they downloaded off the web, how do they know what exactly is being done? I'm not an iOS expert and can't get into the deep down code. So when one JB's the phone, can you be 100% sure something else isn't being introduced into your phone? Example: Maybe a key logger for passwords?
I know there are many benevolent coders out there but I'm also sure some aren't.
You don't. You have to TRUST your source. Same thing with Android in any form, including stock. Many Apps in Android market place have been malware, virus, etc. That's open source for you!
I never had had an issue with the JB community. I am also the guy who doe snOT get viruses, etc on his PC, ever.