Missiles don't always hit their intended target. They can go off course, potentially be hacked, fall into the wrong hands, be sold to mass murderers, fail to explode, accidentally fall out of planes (even nuclear bombs have historically done this), miss their targets, encounter countermeasures, etc.

Nobody is claiming that this was done for reasons of good software design. It's perfectly reasonable to suspect it was done for reasons of cost or plain negligence.

There's a reason tech workers protest involvement of their firms with the military. It's because all too often arms are not used as a deterrent or as a means of absolute last resort, but because they are used due to faulty intelligence, public or political pressure, as a means of aggression, without regard to collateral damage or otherwise in a careless way.

The whole point here is the blase way the technician responded, "of course it leaks". The justification given is not that it was necessary for the design, but that it doesn't matter because it's going to explode at the end of its journey!