Apparently, because this is going to lead to Cold War 2 at the very least.
Also, because everyone on board is from a NATO country. Most of them were Dutch, of whom 154 were aboard.
Other nationalities included 27 Australians, 23 Americans, 23 Malaysians, 11 Indonesians, 6 Britons, 4 Germans, 4 Belgians, 3 Filpinos and one Canadian. The other nationalities are still unknown at the time.
Also, it is almost certain that pro-Russian separatists are behind this. They tweeted about bringing down a plane at the same place before anyone else knew the flight went missing. Massive backpedaling ensued, and now they are claiming the Ukranians did it in a futile attempt to assassinate Putin. No, I am not making this one up.
And the clincher? The black box has been retrieved by the pro-Russian separatists. It has been sent to Moscow, Russia. While zero Russians as far as known were on the flight. They are scummy as fuck right now.