The facts are simple.

The hypothetical situation where professional grade data recovery available to
police defeats the military grade data erasing software available for free to the
public does not exist. Show us one instance where it did.

There's no point anyway because collectors of porn tend to amass large collections
instead of deleting it. Most arrests you see in the newspapers report "huge" collections.

In cases where encryption is used to hide porn, the police either get lucky or they
don't in decrypting the data. Data recovery is not an issue in those cases.

Extreme grades of data recovery are never employed in minor criminal cases.
It's too expensive and only available in matters as serious as murder or national
security. The fact that it takes extremely long times is also a deciding factor
against using it in criminal cases that have statutory time limitations.

None of these facts override or invalidate any other. They go together, adding up
to the simple fact that people who accidentally download something and delete it
right away are never going to be pounced upon by high-tech warriors with magical
abilities to conjure up deleted files and destroy lives. To suggest that such a thing
can happen is irresponsible sensationalism which does the P2P community no good.