What we are actually talking about is you putting your valuables in a safe within your alarmed house and a professional thief breaking in and stealing it. Because the thief previously worked at the safe company and implemented a backdoor in the design.
What we're actually talking about, if we consider security evaluations and ratings, is to...
1. Put valuables in a low-rated safe whose door opener is network accessible and itself low-rated.
2. Whose alarms suck at identifying and responding to actual breaches by even the most common methods.
3. A thief breaking in who uses the most common methods that the safemaker or company didn't try to stop. They did spend a fortune on unrelated stuff.
4. Various designs and implementations that weren't using methods that often prevent or detect backdoor attempts in favor of methods that let backdoors slip through.
Also, this is a company that makes billions in profits a year. They have the money to both develop and build highly-secure systems, including safes. They keep not doing that or not using what high-security they build. They keep using low-security stuff year after year after year. They could defend against those problems by doing more of what works and not using low-rated, often-vulnerable stuff for protecting secrets. Just a hunch on my part. ;)
Morally? No. It's the thief's fault, and the thief's fault only.
But if you know that people steal packages off of porches in your neighborhood, and you leave a package out there for weeks, you're at least being pretty unwise. You're not morally at fault, but pragmatically, yes, you kind of are.
[Edit: That is, your actions are not well-suited for the kind of world that we actually live in, and that you know that we live in.]
Not your fault in a moral sense, but it certainly is in a causal sense.
You could have set up a different causal chain that would have prevented the theft. Of course that doesn't mean that society can't blame (and punish) the thief.
