NASA and ESA want to bring Mars dirt back to Earth, but is that a good idea?

We've all seen it in the plot of cheesy sci-fi: Scientists find something in space that seems harmless so they decide to bring it back to a space station, or even Earth, to study. Things go wrong, and eventually everyone dies. Now, NASA and the European Space Agency have declared their intent to do something very similar, taking samples of Martian soil and bringing them back to Earth. The two agencies are currently planning out exactly how such a complex task will be performed, and it's going to...