It seems to me that a lot of this argument is pointless. It would not be that hard to design a sample return capsule that God himself couldn't bust into for a direct return trajectory. We built a capsule that hit Jupiter at four times Earth escape velocity without burning up. It would not be that hard to construct something that, even if it fell on granite at terminal atmospheric velocity due to chute failure, wouldn't breach the contents. It wouldn't be that much more difficult than doing the sample return mission in the first place--worst case, a Mars orbit rendezvous might be required.

Stop talking to scientists, and start talking to a few engineers.

We certainly don't have to build a Moon base for this, or even add a module to the Space Station.

Chances are very good that we have nothing to fear from Mars samples. Chances were very good that there was nothing hazardous on the Moon, either. Still, why not take a few extra precautions?

I think everyone in this discussion is so hard over on their respective positions that they are losing perspective.