Voluntary whitelisting will never take off. Government whitelisting might happen, but so might government bans. Both are likely to be isolated/temporary, because of the chilling effects they would have on economic growth in the countries implementing them, once Bitcoin is a little more advanced.

Peter Todd is sounding like a codehead, thinking of everything from the technical angle not actual incentives (cypher's meme: "The Geeks Fail to Understand That Which They Hath Created"). There is no slippery slope of incentives for a voluntary whitelist, and that's why it's never been done before. If thieves come to an exchange practically announcing, "THESE COINS ARE STOLEN," the exchange might see it as good PR to refuse them until the coins are better mixed, but if they do any more than that, refusing coins with some level of taint, they just destroy their own business.

There's a somewhat bombastic speech by Stefan Molyneux on /r/Bitcoin today where he points out that if people had to pay directly for the war on drugs, it would come to $XXXXX per person, and people would find their moral indignation fading away quite quickly. I think the same is true with whitelists. The momentary outrage at scammers is not realistically going to incentivize people to make actual sacrifices, especially monetary sacrifices. People might say they'd patronize BTC-e if they only take clean coins, but if accounts start getting frozen customers will make a beeline out of there.

People think they have a strong opinion when they're gabbing on a forum, but the market reveals how much they really care. It's only in government where people's voice on what they think they want, but would never be willing to pay for, comes to fruition.