Not quite true...
Cydia Apps come from Repos (short for Repositories), what that means is that you can install an app from a unknown repo and get a real bad stuff, or you can install from a well known/popular repos and you will be SAFE. like xsellize. Of course like anything else once in a while some malicious developer can leak undesired app to any repo (even the Official AppStore have posted undesired apps). You just have to be smart and dodge em.
Follow your commonsense