As H. G. Wells pointed out, we have battled over millions of years to gain the relative immunity we have from the millions of infectious organisms we share this planet with. What Wells didn't know at the time was the rapidity with which these organisms, particulary viruses, naturally mutate to provide new threats. Our immune systems are not only set up to protect us from existing threats, but from the new ones that constantly pop up.

Even if Mars contained life forms genetically close enough to infect us, the worst result would probably be a form of flu epidemic until our immune systems caught up. As we have seen from the posts, some people even theorize that we are getting alien organic material rained on us every day anyway, and that we are handling this influx quite well. So maybe there is really nothing to worry about. Still...

It's a shame that our propulsion technology is so marginal that the difference between a direct mission and a "careful" mission is so pronounced. Otherwise, there would be no penalty for taking a few extra precautions, which in the real world of industry never hurts when there are no large additional costs involved.

I must admit, my natural instincts, cultivated no doubt by years of cheesy science fiction, are--all else being equal--to be as careful as possible. ("You're bringing that guy with the bug stuck to his face onto the ship????")