Perhaps another helpful paradigm are traffic/construction cones with ‘do not cross’ messages. Sometimes nothing happens, other times you run into wet concrete, other times you get a ticket. They’re just plastic objects, easy to move, but you are not meant to cross them in your vehicle. While concrete bollards are a thing, they are only preferable in some situations.

> documentation clearly states that it's UB to violate them

Only in "fast" mode. The developer has the choice:

> Compilation has two modes: “safe” and “fast”. Safe mode will insert checks for out-of-bounds access, null-pointer deref, shifting by negative numbers, division by zero, violation of contracts and asserts.