long story short if you can execute code on a box it is usually straightforward to get root
The immediate implication of this quote (if it's accurate) is that if you're running a multi-user system and don't try your darndest to prevent all users from creating files with
x permission set, the system is as good as compromised. The corollary is that operating a multi-user system, such as ones typically found in universities, that by design allow all students to do exercises in C, C++, assembly etc, is pointless, since any student can straightforwardly root this system.
Since running computer systems intended to be used by more people than their owners is not considered pointless, and privilege limiting facilities (users' rights management, sandboxing, etc etc) are not considered useless, I somehow doubt these kinds of comments. But what do I know?
Is it true that most Linux systems are straightforwardly rootable by anyone who can execute code on them?