If you read the article, they're raising the concern that we might have the technology to destroy a potential Martian ecosystem before we have the technology to detect it. The question isn't what we currently are aware of, it's whether we might be losing a one-of-a-kind resource that we're completely unaware of.

If there's life on Mars of any kind, that's extremely profound. It would give us a chance to study life on another planet and compare it to our own. It may be that there's no ecosystem on Mars, but it's probably worth it to make absolutely sure that that's the case before we go destroying what might be there.

It may be that we won't have the opportunity to screw Mars up for decades, or centuries. But it'd probably be a good thing if we'd give it some serious thought as a species first.