# Adding an attribute crashes the system?

At some point I noticed the following errors just in the documentation:

And not only this one, this is not only for Manipulate, there were many others. Also the search of the documentation was crashed.

I don't know how smart one should be for tracking the errors like this, but I found what crashes the system mostly by chance, and it is

SetAttributes[FreeQ, Listable].

The strange thing is that mathematica does not warn you anything, when you run this code. So the question is that, 1. is this an appropriate behaviour for the system, why the system crashes when you add an attribute to FreeQ ? and generally 2. how you can make sure that your code (even the small one) does not crush the system, if the system does not warn you about the potential danger, why Mathematica gives you the power that crashes the system ?