I have recently taken an Astronomy course in college, and that is exactly why. No metallic core > No magnetic field > solar winds blow away the atmosphere for lack of said magnetic field. Mars surface is highly radioactive compared to Earth since it has no protection from the Sun. Nothing can live on its surface unless it can be protected from radiation.
It may be a theory, but it is much more grounded in reality than renegade germs.
The truths we are discusssing about Mars also weigh negatively on the silly “science” reports about humans having human colonies on Mars. That would not be possible unless they spent most of their time (70-80-90%) underground and only went to the surface in space suits. And that is just one set of issues that leaves out sufficient water and oxygen.
There are not enough humans that want to live like that.
Mars will always be science project for humans, never a colony.