Thanks very much for all of this. It has been very helpful and a very enjoyable discussion..
I have to run but let me just put this thought out:
In order to release energy, the fission parts have to have more binding energy than the original nucleus (as in fusion: the binding energy of the product - fused nucleus - has to be greater than the original parts if the fusion releases energy). This is possible for U because the fission parts can both be heavier than iron so the total binding energy of the fission parts is higher (which I think is the short answer to the original question).
But isn't the reason the binding energies of the fission parts increase due to electrostatic repulsion? That is, there is a smaller negative electrostatic repulsion term in the binding energy equation for the fission parts compared to original U-235.
Now I understand why your posts have these extra carriage returns!! The system DOES re-evaluate the tex expression, it just doesn't reload your screen. If you use the advanced editor it should reload it for you. Otherwise, just reload the screen in your browser and the revaluated tex graphic will show up..