> Will some bad things happen? Yes, like when humanity learned about atom fission. But the overall result is a net positive: lots of energy for everyone (and yes, that includes Iran) and no world war since then, even with major tensions like during the cold war.
The fact that we haven't (yet) destroyed ourselves with nuclear weapons is mostly thanks to sheer dumb luck, which becomes obvious when you start really looking at the history of nuclear weapons: all the close calls, the combination locks on warheads set to 000000, etc. Using fission as your go-to example of "See? It's OK, we can handle world-ending technologies" is just appallingly wrong, it actually demonstrates precisely the opposite. We can't be trusted with fission and only still have it because political realities mean we can't get rid of it.
Or to put it another way, in any given year there is an X% chance we destroy civilization with fission. X is probably considerably less than 1%, but it isn't zero, and so the Law of Large Numbers essentially demands if we keep rolling the dice without total disarmament, sooner or later they will come up snake eyes. What you want here is to introduce new ELE-enabling technologies, essentially multiplying X by a constant. Madness.