It's the wrong metaphor. The Maginot line was supposedly impenetrable for keeping clearly labelled troops on the other side. The modern situation is something much more porous, much more like Cold War (counter)intelligence. Or this discussion of "interpretative superiority": http://www.harrowell.org.uk/blog/2018/02/18/why-corbyn-is-th... (although I disagree with the conclusion). A system that can detect ideological incursions, vector an intercept response, and shoot down memes that get over the line. Analogy between forum moderation and those Phalanx CIWS systems for shooting down missiles.
The West doesn't have a central ideological defence system though, or at least not since the Cold War. Instead it's more like an immune system. Individual agents wander around the body politic attacking ideas they find unfamiliar. Responses to ideological challenge happen not through central coordination but by the actions of individual and factions.
The effectiveness of this system has become an autoimmune disease that can be exploited by pathogenic actors. The US police are a good example of this: their ideological defence is so strong it can cover even crimes committed in broad daylight on video.