In the weather we had it could have been locked.It operates all day with much more stress on it.It's just the done thing to let it slew.Either way,if you can't see it.It's dangerous.Time will tell if the experts deem it was safe.
I am sensing an utterly absurd undercurrent here that the problem that needs to be solved is development in London providing an obstacle to general aviation.
That carthorse you see over there? It's not going to work that way round.
In the world you envisage in which London is preserved in aspic for the convenience of aviators, the demand for aviation of any kind is going to drop to zero.
There are doubtless many lessons to be learned from this awful incident; "we should ban cranes [and by extension development] in London" is not one of them.