X-51: Speed kills?

Isn't that just the coolest thing on Earth? Er... no it isn't. But it does sound great. Meet the X-51, US's latest weapon in development. Billed as the successor to the super-successful and ultra-accurate Tomahawk, the X-51 will be much, much faster. 5 mach. 3600 mph. The Popular Mechanics/Gizmodo posts suggest that the missle won't actually need any explosive content, since crashing into anything at 3600 mph is a guaranteed result. Lovely.