If law enforcement can develop tools and techniques to catch criminals using bitcoin they will have effectively proved that bitcoin's implementation does not provide adequate anonymity or security.
I disagree.
Just like Tor, bitcoin can never be 100% anonymous. An investigation team with enough manpower and time on its hands can track down
any bitcoin user, with one exception: The bitcoin user who never spends a single bitcent in his wallet.dat. But what use are bitcoins if you can't spend them?
However it is anonymous
enough for most people going about their daily honest business. Discovering the identity of bitcoin users takes a large amount of resources, so governemnt will only ever bother going after serious criminals, while ordinary people can enjoy the benefits of financial privacy.
Whether or not you agree with what certain people do with bitcoin, it's purpose is to prevent ANY central authority from having control over the financial system. This includes governments. If a government has a way to prevent, manipulate, or track transactions at will, then bitcoin will have no purpose whatsoever.
They can't control Bitcoin itself. All they can do is prevent selected individuals from spending their bitcoins using traditional police work.