Yes, it was on purpose, but it wasn't necessarily all about launch authority. It was military disagreement with civilian government over how to implement contradicting policy and law, regarding security, safety, and readiness.

The government (executive + civilian agencies) saw it as an authority (command/control) issue, but the military saw it as readiness and ability to always respond to an attack.

In the context of flying bombers around the clock to ensure a first-strike survival, you don't want to have your counter-strike hindered by a misplaced code. This was also before the survivable comm systems were fully deployed, so some autonomy was required to ensure MAD as a deterrent.

Anyway, there was a government mandate for the bombs to be secured with a code. The military commanders didn't want this, saw it as impeding their mission, and instead of fighting the rule, they "complied" by implementing the systems, then loophole-ing it by setting all zeros.

To elaborate some on the military thought process: The previous methods of arming were more about safety than security (ensuring the bomb wouldn't be armed during takeoff/ landing, a crash, in the event of a bail-out, etc). One design was pulling a pin to drain ball bearings, but was mechanical and failed too often. Also, I believe it usually failed safe (or uncertain), which the military also saw as a problem.

Before that, the package actually had to be installed (or at least opened and activated) in flight. Which had it's own problems.

Point being, the military had spent years trying to streamline the arming process while making it more reliable, and now they had to comply with a rule that they viewed as unnecessary and in contradiction to their stated mission of readiness.

There was also a political struggle of bomb custody, as initially the bombs were to be (and were) in the possession/control of a civilian agency, and only a fraction in possession of the military at any given time (during peace). So there was some ongoing tension from that also playing into things.

To borrow from Dan Carlin, there was some logic to the insanity.

The whole history of it is fascinating, and this is only one tiny aspect of one of many many topics.