No, Building 7 was just poorly designed. I used to find it a compelling point, then I actually read about how poorly thought out it was. They built a 40+ story building on a foundation meant for 25 stories, it’s surprising it lasted as long as it did.

No, it's not true. You wouldn't ever use magnesium for that anyways, you'd use an actual demolition charge if you were dumb enough to rig every tall building with explosives. But no, nobody is that dumb - the kernel of truth at the heart of that one is that some large buildings have demolition plans drawn up when they're constructed (important note: the WTC didn't have that, it's both very rare to do and a much more modern practice than the WTC buildings), which are just a reference for if/when the building is demo'd in the future. They're not rigged to blow, though. Hell, aside from all the obvious reasons you wouldn't do that, chemically most explosives would become uselessly unpredictable after being strapped onto a building for that long. Just an absurd idea.

Like a system like the swiss bridges? They have marked points but don't just leave the charges on the bridge. It flies in the face of conventional engineering to plan a failure point on something that should never fail. So all building are wired to go at any moment? You would think there would be a few more accidents and this would require a large and obvious agency to manage and monitor in secret. Considering how much demolition work costs it is not "easy" to bring a building down.