The Viking results were at worst, inconclusive and at best positive. And yet in both cases we have been led to believe they were negative. They are far from the only pointers to life on Mars either, since we've seen pictures of what look like fossilised stromatolites and algal mats, seasonal methane emissions, and discolorations in seasonal flows & ice.

Even the rusty coloured surface of Mars may be due, in part, to organic oxidisation processes.

We aren't talking about Richard Hoagland style cities here (although that Face on Mars is a lot less easy to explain away that some people claim).