The issue, as they saw it, was that up until relatively recently, GPS was the only option. Not only did the US military and civilians use it, but foreign forces probably used it as well... maybe even potential adversaries. In a conflict, they wouldn't attempt to disrupt GPS because doing so could actually hurt their own operations. That assumption changed once GLONASS, Galileo, and Beidou (plus the other regional networks) started coming online, all at slightly different frequencies. And, just like the US gives military-grade GPS equipment to its allies, the operators of those systems were probably doing the same, making it more likely that in a conflict someone somewhere will be disrupting GPS because they have another option for themselves.

From a civilian perspective, I'm not all that worried about GPS jamming. Yes, it's disruptive, but most organizations and systems that rely on GPS for navigation or timing (GPS is just clocks in space) should have training or failsafe fallbacks by now, to at least provide a temporary alternative. What does worry me is GPS spoofing. This is why the military has encrypted signals for its own and allied use.

I'm sure the Economist article mentioned all or some of this, but I don't have a subscription.

Edit: Typo fix