First, why was the idea so popular to begin with? Collective funds aren't new, nor is using Twitter as an API for tracking things in the real world. I don't have any good guesses here.
Second, why has the community reacted so passionately? Even here on Hacker News, mostly made up of people who put reason over emotion, have been extremely upset. One: Having the money taken broke people's faith in the greater good of humanity, so indignation naturally follows. Two: Diverting funds was akin to telling people what to do, and nothing makes people angrier than being forced to do things against their will.
People got very emotional over what, in perspective, isn't that much money. $625 could get you an iPad... or a really lousy computer. If somebody had that much stolen from a home break-in, that wouldn't even make local news, let alone Hacker News. It's very curious. Also, it shows money not just as a means of gaining goods and services, but as a way for people to make a mark on the world; 'voting' for things they believe in by giving money, and denying it from things they don't.
I don't approve of what Sam did, but it's better to step back and really see what's going on here, rather than just being a mob about it.