I suspect whoever used free will as a component in an argument about MWI was somewhat confused.

I used it, and was confused. I think something fundamental to ethics (maybe free will?) is incompatible with modal realism, and was considering the thought that it's incompatible for the same reasons with the kind of realism concerning the mathematics of non-relativistic quantum mechanics which produces the MWI. I didn't make any real headway, but quite a few people said that MWI couldn't in principle conflict with the possibility of free will because of Egan's law. I'm here objecting that any interpretation of Egan's law on which this is a valid argument must be false.