1) You avoided the main issue of your self contradiction. Thois tends to make people suspicious of you.

2) Re your point 1:

a) RE "You can still contract diseases from other parts of the world (Earth) even though these germs have shared our planet with us for millions of years. So why would Martian grerms (if any) be any less harmful than our own?"

You have the argument of your critics exactly backwards. It is precisely because we have shared a world with certain microorganisms for millions of yeras that they are pathogenic.

b) RE "You cannot prove they would be harmless,

Of course not. And we NEVER will no matter how many probes are sent to Mars. You can't prove a negative finding permanently. You can't prove life exists there let alone even suggest any rational reason why it should be harmful. All that anyone can do is evaluate the odds of one position vs the other given what we do know.

Despite your frequent distortion of their position the NRC has assesed the probability of both surface life on Mars and the independent probability of it being hazardous as near 0. Despite that they recomemnd as a matter of STANDARD scientific protocol that unusual unknown material be treated as
hazardous. Your whole position ignores that we know how to handle the most hazardous organisms known safely. This makes it a moot point even if in the extremely low probability event that Martian organisms exist and are hazardous.

c)RE: "otherwise the National Research Council would not have issued it's most recent report stating that an appropriate Martian Quarantine Facility would take ten years to build."

Another misleading comment. The recommendation for a new facility was to ensure both containment and no contamination. They did not state that current biohazard facilities were inadequate for containment reasons. They stated the two goals were somewhat contradictory as one typically relies on positive pressure while the other often relies on negative. As I have poointed about before the retun on investment in such a facility is very low because contamination issues with existing containment facilities are already low or the research threir would be worthless. A much simpler solution is a positive pressure box inside a negative pressure building.

3) RE: your point 2. I know you have a copy of the one here:
http://www.planetary.org/html/news/articlearchive/headlines/2000/swappingrocks.html . Zubrin's rock argument is simplistic for some of the reasons you mention but the article you site came up with a nonzero estimate for the amount of material meeting the requirements.

The article you site clearly states that "They select conditions that optimise the chances of lifeforms surviving the journey" and "These criteria are likely to be very conservative and therefore serve to set a lower limit to the exchange of hospitable rocks between Mars and Earth". It reduces your credibility to claim optimum conditions are limiting ones and that lower limits are upper limits. Once again you have gotten the technical arguments exactly backwards. As with all matters of probability there is no exact time at which the probability of viability reaches 0. Siting articles which "prove" your point which in fact do not is another reason many hold you in low regard.

On a final note YOUR source states "Under this scenario the quantity of "hospitable" ejecta reaching the Earth from Mars averages out at 150 kg per year. This represents roughly 15% of the total estimated quantity of Martian material falling to Earth each year."

RE: " if the Mars Society is a non-profit organization, why does Bob Zubrin sell his books in every room of a Mars Society Convention? Are the profits from the sales of his books going straight to the Mars Society or his bank account?"

In the past he has donated his portion to the Mars Society. Whether or not he still does I don't know. So exactly how much have you donated from your profits and due your sales increase everytime you get airtime to spout your dangerous microbe theories?

Regards,
Mark

PS Since you like Sagan so much that you support even his dumbest ideas like testing MSR with anthrax I suggest you read his book "The Demon Haunted World" and look up the tools in his scientific baloney detection kit. Many of your detractors are equiped with something similar and you might hone your arguments better if you learned to apply it to yourself.