They gave a massive buyout offer before copying. There was only one thing left to do after that.
Or that it is better for public interest that people prop up companies with multi billion dollar valuations on the basis of trivially copy-able features?
It is harmful to the public interest to allow a company to use its monopoly status as leverage to monopolize other markets. Facebook is competing for image messaging in the same sense that Lance Armstrong was competing in the tour de france.
Monopoly is the degenerate case of capitalism, and this kind of behavior by monopolies is how the degeneracy reproduces.