[ceejayoz]

> That would be true if we were looking for life currently alive on mars

I mean, why not?

> Fossils would survive a million-year trip just fine.

Sure, but getting to pick where we take the rocks from helps us maximize the possibility of fossils in the sample. The rovers have found rocks with evidence of water - being able to pick those instead of a random chunk (which might've been blasted from deep bedrock) found in Antarctica has its appeal.

> There has only been one serious attempt to detect current life, the labeled release experiment on the Viking lander. It came back positive.

This seems like a good argument for sample return.