Dear The Economist,
Admittedly, Mars is even less hospitable than the Atacama. Besides the aridity, the Martian surface is bitterly cold and blasted by solar radiation. That radiation creates powerful oxidants that would likely destroy any living cells. If anything does survive, it will be deeply buried. That is one reason why the ExoMars rover—built by Roscosmos and the European Space Agency, and due to blast off in 2020—carries a drill capable of digging almost two metres below the surface
"If anything does survive, it will be deeply buried." : this cannot be asserted that positively. New evidence since 2008 suggests there be possible habitats at the surface where Mars life, it it exists, could be metabolizing and/or where our earthly microbes might be able to metabolize as well.
So we cannot rule out the existence of habitats where life can metabolize on the Mars surface. And I do mean surface: many ideas of such surface habitats have been suggested (salty seeps, melt water under clear polar ice, ice fumaroles, dune bioreactors, among others).
There's a wide ranging debate about Mars and about whether the proposed habitats exist. So your statement is about a decade out of date although some would still say it today so either a decade out of date or a personal view which if by someone up to date on astrobiology they would recognize as their own view in an extensive debate.