I believe I know enough about the positive arguments, and in general I do not dispute them.
Unfortunately there are negative or highly uncertain arguments and I have still to see good answers to them. "Selling" articles like Mark's generally avoid them.
The risk of bitcoins being stolen (possibly en masse) by hackers is an example.
An example of what? There is a risk of <INSERT NAME OF ANY CURRENCY HERE> being stolen en masse, in exactly the same way. This is not a problem unique to Bitcoin.
Bitcoin is only one cryptocoin. Why should it be the one to survive?
Did you actually read the article? He discusses this at length, focusing on network effects primarily.
Non-cancellation may be good for merchants (especially dishonest ones) but is bad for customers.
As is true of cash in any currency. Again, this is not unique to Bitcoin.
Governments can ban, restrict, or heavily tax cryptocoins if it suits them.
That is a possibility. Some governments can do damn near anything.
What will prevent banks and Wall Street from taking control of Bitcoin?
I will have to refer you to the original whitepaper here. Success is not yet proven, but so far it's looking pretty good, I think.
How could the value of a bitcoin be stabilized enough for merchants who thrive on 2% profit?
Again, I have to wonder if you really read the article. It addresses stability concerns very well, and shows how many merchants with low-margins can seriously benefit by avoiding CC processing fees.
And so on...