You didn't understand the sentence you quoted, not at all, and your own first sentence has absolutely no logic.
You assumed that OS is one thing, which is a bad assumption. Then you reasoned: if it is not secure to call A, then A is not secure.
The fact is that OS is not one thing, it is many things - many layers. It is insecure to call layer B if you bypass layer A that was supposed to provide security.
read my oppinion that I just provided as reply to one of tilly's post... really people should learn some philosophy and logic.