I don't think the author is suggesting we shouldn't build useful things. He's saying to the people who built the military system that they shouldn't be doing that.
It's the last step that's the problem, not the people who built all the things they stand on. Otherwise we'd be suggesting that no one build a database engine or a digital camera or a computer ever again in case they're used to build evil tech.
They're not confessing, they're bragging
Not sure about digital cameras or database engines, but computers and the Internet were, in large part, created for military needs first and foremost.