Sure. My argument isn't about there being any particular probability of a harmful outcome. I expect the probabilities to be extremely low.
But extremely low doesn't mean zero, and in this case, there are very large unknowns. The question is not whether to ever send people. The question is when.
For bringing rocks back from asteroids, since we have no evidence of life there-on, the risks seem negligible. For a structure on Mars which is a bona fida manufactured thing, the evidence of life is a given. Since the locale is Mars, the life is probably (but not definitely) a different lineage than our own. Mars has very different qualities compared with the Earth: An organism adapted to live there might do terribly on the Earth. But, organisms might be adapted to Mars of a different era, and be adapted to a more similar environment. Or there might be that odd chance that the organism can handle an Earth environment.
If I change this around: Let's say a Rover scratches its way to a subsurface layer which is teeming with life. No alien structures, just an unknown but definite collection of biota. Should we plan on sending people to study it before sending probes to do a careful study beforehand?
Given current technology, I imagine we must send probes first, simply as the only currently technically feasible option. That means probes first in any case. Would we start planning immediately to send people, or wait for the results of the more advanced probes?
Thx!
TomB