"The boffins paint a nasty picture and just killed a thousand dreams"
well, there's still the possibility of terraforming, but that would take a LOT of effort with tech we don't have yet.
The best theories I've heard suggest that Mars lost its magnetic field because of a mostly-solid core. If the core were liquid, mars would have 'van allen' belts too, and its atmosphere would (mostly) still be there.
Without volcanos you don't replenish your atmosphere. Mars doesn't appear to have active volcanos in any significant amount, not like Earth.
So: to "fix" Mars, you need to melt its core. How to do that? Oh, I dunno, maybe a few hundred ATOMIC BOMBS or something like that. It is, after all, a planet, and melting its core would require quite a bit of energy.
Mars has a LOT of evidence of flowing water and thicker atmosphere at some point in its history. Nowadays, it's almost a vacuum as far as atmospheric pressure goes. You'd need some pretty strong pumps to suck that in and make it 15psi for human aspiration (assuming the O2 levels were correct). Pure O2 would have to be at least 3psi, just sayin'.
Anyway, the 'past life on Mars' stuff has mostly hinged on the idea that at one time in its history Mars was a LOT more Earth-like, and I tend to believe that the science supports this.
As for terraforming, you'd have to fix the core first. THEN, "borrow" gasses from someplace, and transport it to Mars, plant some, uh, plants, get some algae to grow in bodies of water, and there ya go.