Eliminate 40+% (two or three points) of centralized accumulation in the form of wallet, therefore BTC, destruction, preferably after the reward halving. Repeat until reserves are exhausted and only p2p trades are "reliable".
Watch the destruction of any economy, especially fragile fledgelings.
All that would be needed to counter this is an extension past 8 decimal expansion. As computing power progresses, older keys can be cracked, thus restoring access to 'destroyed' bitcoins.
Pollyanna would assert that the divisibility of btc would merely shift the decimal point after such a catastrophe, but there is no traditional economy upon which to base the value of BTC. Every government that has followed this path has been declared a 'failed economy'.
None have ever relied upon market forces to adapt their currency value, neither have they ever shifted the decimal to the right - only to the left. Gold was the only form of money to accomplish this, and economies based on the gold standard only destabilized because of limited practical divisibility.
hazek is right, most of Bitcoin's value derives from its convertability with fiat money exchanges. If this goes, so does lots of its value as well as usefulness.
The comparison with alcohol or other drugs is idiotic because these goods' value derives from its consumption, not from convertibility with anything. Therefore, when production cost rises due to legislation, the price in the longer term will have to rise too, or else it cannot be profitable to produce.
Actually, notme is more right in the long-term. Currently, association with value is highly related to exchange rates, the most prevalent being the US dollar. As the Bitcoin economy grows, it will become less dependent upon external metrics and be used as a measure of wealth itself. That is simply a change from items being priced in $ to being denominated in
BTC.
As for the comparison, it is not entirely accurate, but it is still very valid. The incentive for use can be far greater than the legal risk, resulting in elevated demand. If there is anything that can be supplied to meet the demand while returning sufficient profit for the risk, it will be provided. Money is no different, it just has a more nebulous use case because it is universal. For an example, just look at any country with a deteriorating domestic currency which outlawed the US dollar or gold, yet experienced rising use of them among the population.
All of the other methods so far have been too 'centric' - as in, focused on a country or region. Cultural, societal, and even genetic variations guarantee that you can't fool everyone all of the time. If Bitcoin continues to be seen an improvement over what exists now, it will keep growing no matter the opposition. Period.
Targeting the developers might be more effective; attacking the vulnerable pseudo-head instead of the amorphous body. Until Bitcoin is at a point where usage is widespread enough that most people are familiar with it, and no new technical threats are both foreseeable and realistically feasible, there are a number of ways to erode but not destroy the system.
and this goes for most people alive, like 99% (% pun intended 
)