Oh please. Some of the good apps in Cydia and other sources have pretty crappy documentation and warnings, let alone the poor ones. And a change log does not a comprehensive explanation of warnings and potential system performance impacts make.
You can say it as many times as you want. You can say the ocean is yellow and the sky is green. Aside from the fundamental fact that the user does choose to install the software in the first place, what messes up a jailbroken device is the nature of so many apps available for these devices.
The same Apply to your logic, you can say whatever you want but getting root access to a system (A.K.A jailbreaking) Do not slow down or add instability to the system, users that don't know how to read do. Not sure what you are talking about, all the mods and App are use have Changelogs and Warning for any Known bug or issues. The "fact" is that user mess the system up no the software or the act of jailbreaking for that fact.