Alex,

Zubrin has a rational basis for his view which is admittedly not iron clad. His pathogen analogy is based on an "as far as we know or at least very seldom this doesn't happen basis". He leaves out some alternate negative biological scenarios of possible concern, but none of these approach the scale of Digregorio's scare tactic scenarios. Digregorio postulates scenarios for which there is no evidence for and good reason to believe are not possible then uses these to justify his stance. Saying the truth lies somewhere in between is a grossly misleading statement.

Digregorio doesn't seem to be aware or at least won't admit that many of his scenarios are mutually contradictory. He seems to believe that all the possible bad outcomes should have their probabilities added together despite the fact that many are mutually exclusive.

The biggest problem with BD is bald faced lies such as:
-Levin discovered life on Mars and only a NASA conspiracy keeps other scientists from admitting this.
-Claims that there is evidence for hyperdisease caused extinction.
-Misrepresentation of the scientific consensus on how fast the dinosaurs died out.
-Denial that there is good reason to believe that life could have survived a trip from Mars to Earth inside meteorites while at the same time supporting claims that unprotected viruses from sopace could cause flu.
-etc, etc, etc.

We have a person with no technological credentials who frequently spouts nonsense and often parrots without thought his idol Levin versus a PhD Engineer with demonstrated technological and creative skills who is in frequent contact with many leading astrobiologists. Do you really think the truth is even close to half way between them?

Regards,
Mark