Where is this point of view coming from? What you are saying is just contradicting the GPL2:
Let me quote it:
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
You may modify your copy or copies of the Program or any portion of it…
and so forth. The GPL2 is very clear. You have all rights to change the source and distribute it.
I am really concerned that the result of this FUD campaign is that you do not dare to patch the source code. The GPL2 is giving you all the rights to do so.
Who told you that you are not allowed to change certain parts of the source code? You are allowed to patch anything as long as the resulting source code is under GPL2 license
EDIT:
Good read about this topic: What is Free Software? - GNU Project - Free Software Foundation