Why Are Offshore Accounts Considered Such a Bad Thing?

I think financial privacy is a good thing since predatory governments are less likely to misbehave if they know taxpayers have safe (and confidential) places to put their money. Now that privacy has been weakened, however, anti-tax competition folks at the OECD are openly chortling that there can be higher taxes on capital.
The bottom line is that tax competition without privacy is not very effective.