I stole the title from a question raised by Stanley Kurtz of the National Review
http://www.nationalreview.com/kurtz/kurtz200401120904.asp

Will we SEND people to Mars, yes.

If we think there may be life, past or present, we'll send humans sooner. But even if it's just a geology mission, or just to plant a flag, we'll go eventually.

Since the main driver will be politics, not science, the possiblity of life doesn't have an overhwhelming effect. For humans on Mars by 2050, I'd say 40% if the current "warm, wet, and unsubstantiated" paradigm holds; 20% if it's dead, Jim; 80% if we find both old aqueous sediments and evidence of ongoing hydrothermal activity.

Eventually, though, we'll go. The "because it's there" draw is just too powerful. If technological civilization does not collapse, we'll eventually develop technologies that make going to Mars easier. Right now Mars is so expensive that you have do a good job of proving the case for why we should go. At some point it'll become more like Everest or the South Pole in the 20th century -- why not go?

Will we STAY, however?

How many people live on top of Everest?

How many people live in Anatarctica?

Better yet, how many on South Georgia Island, which had a thriving little whaling community in 1900, but only penguins today. Or in the "Empty Quarter" of Saudi Arabia, northern Siberia, or Devon Island?

Some do, of course, involved in extraction of exportable resources, scientific research, military bases, penal colonies, etc. Outposts that generally vanish as soon as the external support ceases. I can imagine Mars having a permanently crewed research outpost, but what beyond that in the next hundred years or two?