If dark matter has some way of interacting with itself, then dark matter particles could collide and turn into particles of normal matter, just as two normal matter particles can collide to create dark matter.
This is puzzling. The presumption here is that if you can make one thing out of two other things, then you can make this first thing out of these new other things. It may well be the case and the law on the particle level, however, in my experience you can't turn orange juice back into an orange.
