I'm definitely not in the "speculators are evil" camp. Speculation for the right reasons (hedging risk, for example) is a very good thing.
I personally think speculation for the thrill of gambling is not a good thing, but I'm also not in the "Every Bad Thing (where I get to decide what Bad and Good is) Should Be Illegal" camp. If you want to gamble you should be free to do so; I think it is stupid that we let rich people on Wall Street gamble with other people's money and yet have laws that make it illegal for not-so-rich people to gamble with their own money.
From his post, Tong thought about Bitcoinica and decided that he could be more effective at making the world a better place by working on something else that is more obviously positive-sum. Good for him!