The genie has a hard time calling it "replacing" blood with molten salt with blood making up so much of the human body and what is left destroying itself almost instantly when exposed to molten salt that all you'd really get is a molten salt shaped human and some bones in a pile after. genies also pretty sure the moment he poofs away the blood there already dead so this is just an over complicated way of throwing someone into a molten pit of salt. Your going to have to trust the genie on this one.

The quantity and speed govern energy, remember the genie was just confronted with the worst of humanity what if the genie decides all of humanity needs a reset with lots from everywhere destroying us all?

This is why the genie was worried, asking a genie for revenge or destruction almost always goes terribly wrong if only on principle of the genie not bring a hitman and is looking for equal ways to turn it against the wisher.

Using the sign of the red cross when you’re not The Red Cross constitutes a violation of the Geneva convention. I.e. a war crime.