I guess in the future, the network can develop a mechanism to mark "bad" address and then avoid taking payments from such address, today there is no such mechanism (I guess bigger thefts can be tracked and nothing can be done with them).
No, bitcoins are cash, there is no possible way to make such a thing work.
I disagree with this statement, though I'm aware to the fact that there are many problems with such approach - mainly, how do I prove that this is theft and not transaction I did.
Resolving these problems will make Bitcoin theft irrelevant and enable better security, and from feasibility point of view it is not hard at all.
be solved, period.
Cash is cash is cash. Or it's not cash anymore.
If someone steals 1 dollar and then uses to pay a few apples at the groceries, you can't take that dollar from the grocery store, or the concept itself of cash is dead.
So, no tainted coins.