Planetary overprotection: Have we made ourselves Mars' helicopter parents?

We've talked here before about the Office of Planetary Protection and efforts to make sure that we Earthlings don't contaminate the rest of the galaxy with our bacteria, viruses, and other assorted detritus. Now, some scientists are arguing that we've done this job too well, effectively barring ourselves from exploring the parts of Mars that are most likely to be hospitable to life precisely because they could also be hospitable to tagalong life from Earth.