/etc can be entirely readonly to most apps, many of them also either wont start from root or drop permissions right after loading.
That is not the case for registry, far more ways to fuck up.
To delete things in /etc you will be asked to gain root privilege. It's usually one click (You might be asked to confirm your password).
Deleting things when admin/root can break things in both cases.
Let's just admit it and move on.
The paragraph you quoted is in context warning the user about MANUAL intervention in the registry, that requires privileged access. So we aren't comparing it to "what can random app do", but what can super user do.
/etc can be entirely readonly to most apps, many of them also either wont start from root or drop permissions right after loading.
That is not the case for registry, far more ways to fuck up.