If anywhere this should be solved at the protocol level, not at the social level. The bitcoin system should be completely agnostic about the intention of a transaction.  All it should be concerned about is the total cost of a transaction, both to the miners and relay nodes.

If people start using patched clients to block transactions based on perceived intentions, we are going to get into a huge mess.  Players like Satoshidice are going to start obfuscating their intentions, resulting in arms race, and before long there will be collateral damage, and innocent people who's transactions look like their intention is X,Y and Z are going to have them blocked.

It's going to be a bit like the old financial system. After some players misbehaved, government introduced rules like 'trading X with the intention to speculate is prohibited'.  Of course, this didn't stop traders from speculating, it just encouraged them to repackage their financial instruments to make it look like it's not speculation.  

These intention-based rules only make the financial system more complex, less transparent, less fair, and less stable.  We really don't want to do the same to Bitcoin. Let's keep it simple please!