That they shot an asteroid from halfway across the galaxy and managed to hit, not only another planet, but the planet they actually aimed at, is not just impressive, its goddamned miraculous. Especially considering that the Arachnids don't seem to have much knowledge of math and interstellar travel -- their species spreads to other planets by shooting their spores into space and hoping for the best. In fact it's so amazing that it's either a plot hole or a surprisingly subtle plot point- there's a theory among Starship Troopers fans that the attack was either a random collision that the government used as an excuse for war, or a deliberate attack by the government on its own people to justify attacking the bugs.
Either way, humanity promptly loses its shit and declares war on all bugs everywhere.
"Well this seems easy enough."
In Real Life:
You can see right away how the plot mimics real events. Before 9/11, the threat of Islamic terror was lingering out there, but wasn't immediate -- just like the bugs in the movie. Then there's an attack on a civilian target that comes as just as much a shock to the system, as it demonstrated a capability no one thought the terrorists had. The US promptly lost its shit and declared war on the very notion of terrorism, entering into an armed conflict against an abstract concept like only America can.
"And after we beat Terrorism, we're gonna beat Drugs! Then we're going to take on Sadness!"