You are asserting that security has to be hand-crafted. That is a very strong claim, if you think about it.

Is it not possible to have secure software components that only work when assembled in secure ways? Why not?

Conversely, what security claims about a component can one rely upon, without verifying it oneself?

How would a non-professional verify claims of security professionals, who have a strong interest in people depending upon their work and not challenging its utility?