You do realize the lengths states like Iran are going to enrich enough Uranium for a few simple bombs? If this works as a shortcut, it doesn't have to be easy or practical. And besides, it might be a lot easier if you don't care whether the people cracking the thing open will survive the ordeal, or whether radioactivity gets released to the environment.
If you treat these things like nuclear weapons they won't be very useful. Securing those bombs is enormously costly. You can't do the same for thousands or more of such reactors deployed for decades, all over the world, under civilian control.
Given that even the US Military doesn't have infinite resources, how can you guarantee there will be a fast response, or any response at all, or even that anyone will notice 20 years after deployment if someone with the resources of a nation state tries to get at that Pu? There might be wars where that reactor is deployed, there might be natural disasters, people might switch to 100% renewables and lose interest in the reactor, ...
