Curiosity's inability to find methane might be a blow to the idea that there is any life on Mars. (It might also mean that the gas is trapped underground and/or only in the atmosphere very locally before boiling off into space).
I think that we keep clinging to the idea of life on Mars because of the romantic image of the canals, even though there are many places in the solar system far more likely to harbor it (Titan, Io, even Venus is more likely than Mars). Mars has always been the place the 'other people' live...malevolent in War of the Worlds, benevolent and strange in Stranger In A Strange Land and Out of the Silent Planet and, of course, just like us on John Carter's Barsoom, with all of the same problems and conflicts.
We want there to be life on Mars so badly that we ignore any and all evidence...and if we can't find it, then we have a strong desire to put it there. Perhaps even to put ourselves there - and it's true that Mars would be the easiest place to plant a colony.
Even I can't quite let go of the hope that we'll find something, even if it's only bacteria. Mars is simply part of the common imagination of western culture. We want that planet to live.