Re: Spot on
Ultimately unless it's fully secure it's not secure.
No non-trivial system is ever "fully secure". The phrase is essentially meaningless. The security of a system is the probability that it will behave as intended (itself a nebulous concept) by authorized users (another one). That probability can be reduced by accident, faults in the system, and malice; for the last category, security reduces to the economics of attack.
So for any non-degenerate case security can only asymptotically approach 1, and in fact because of the difficulties of defining "intended behavior" and "authorized users" (many of which will not be human but other systems to which we've delegated various functions), the goal can't even be defined with decent precision.
And so talking about "fully secure" or "perfect security", etc, is nonsense. You're appealing to a concept that isn't even theoretically sound, much less realizable in practice.
And thus by your formulation nothing is secure at all, and any discussion of security is irrelevant.
Treating security as a binary is pointless. Don't do it.