If we don't sterilize our craft, how do we then verify either that life arose independently on a non-terrestrial surface or that ejecta carried it? Hopefully the value of sterilizing our craft becomes apparent as one considers the scientific value.

You'd think so, but the structures in the rock show it was never heated enough to be entirely sterilized. That was a possibility people had previously hypothesized about, but not something that had previously been proven.

You have pointed out how my third paragraph contradicts my second. Thanks. :)

Bacteria surviving on the rock would need to be buried deep inside to be shielded in such a way, and eventually break out to the surface.