Quote from justrading:
You could also look at it differently.
If the FTT is adopted globally, there are certain implications, eg reduction in transaction volumes, reduced profitability and reduced taxes collected, etc etc.
If the FTT is only adopted by certain countries, you can add to that list migration of financial activity to other countries where it would be cheaper.
To paraphrase Osborne, adopting the FTT globally would be bad, adopting it only in certain countries would be ruinous.
The negative implications for society would be more profound than "reductions in transaction volumes, reduced profitability and reduced taxes collected."