Ethereum is experiencing a classic "too big to fail" scenario. Imagine a country establishing themselves after a revolution. They start printing currency, and for some reason tons of people decide to invest lots of money in the first investment bank to crop up. It turns out, that bank's bylaws allow anybody to walk in off the street and get the bank to invest a small amount of money in the company of their choosing, and they can do this as many times as they want. The first unscrupulous character to realize this manages to siphon off all of the bank's money, screwing all the investors. He does it anonymously so the law can't take him to court, and it's not entirely clear whether what he did was illegal--he didn't steal the money: he just convinced the bank to give it all to him according to their own policies. With the only major institution in the entire country facing certain bankruptcy, the value of their currency collapses.
In this situation, the leaders of this new country might decide that, even though this crisis was technically the fault of the bank's leadership and dumb investors, the credibility of their nation and its currency is at stake. Allowing things to go unchecked would hurt not only the dumb investors, but all of the citizens and foreign interests who had invested in the nation in any way.
The good news is that this country's currency works in a way that they can choose to reverse the transactions caused by one bad actor. Maybe they can't catch him, but they can seize his assets, dissolve the investment bank, and give the money back to its investors.
There are a lot of valid arguments against them doing this. For one thing, they'd have to pass a new law that's specific to this one incident, not because there was anything wrong with their law in the first place but because they want to punish one bad actor. Also, this sets a precedent where people can expect the government to seize the assets of public enemies and come to the rescue of bad investors, as long as there's enough public support for it. What began looking like free-market democracy suddenly begins to look more like communism. Foreign investors will be hesitant to bring their money to a country that acts that way.
However, the damage caused by doing nothing will likely outweigh the damage caused by this action, so the nation will probably enact this law, especially since voting power is based on how much people have invested in building this nation's infrastructure. Contrary to popular belief, the block chain is not a democracy: it is an oligarchy.