If I don't trust security in the low levels of the stack, why should I trust no security in the low levels of the stack? If I'm not certain of the low levels I

If I don't trust security in the low levels of the stack, why should I trust no security in the low levels of the stack? If I'm not certain of the low levels I can always add security. Why not just have security in the low levels so you completely eliminate insecure communication. Security by default.