>>23444914
>A properly built O'Neil Cylinder would be built so thickly
Many things wrong in your argumentation.
1) thick won't solve that problem, it worsen it because it's more mass, more strain, less room for mistakes as you approach construction limit, you'd actually create explosion vents so you don't need to contain an explosion.
2) the only sources of radiation that matter are the sun and nuclear reactors, one is unidirectional and don't require rotating shield, the others are shielded on their own by UC level of technology.
3) properly built mean cost-efficienty, only preparing for reasonable danger. That's why suspended bridges aren't built to resist a nuke or even a military grade explosive.
4) finally, all part of a colony aren't equal, the most critical part would be the spindle, damage it and the entire colony start disassembling itself.

Even if the advent of the Federation wasn't supposed to mean less war, there's no reason to waste money to survive a genocidal war when having multiple colonies far appart on unstable Lagrange point is already providing redundancy.

Also a proper colony (even 3 islands one) would likely have plenty of interior tethers, both for structural reason, for practical construction needs, not just copy artistic illustration of what they could be.