[narf poit chez BOOM]

I think it is quite close to Sci-Fi canon to treat aliens as a thread and go to the war. Every time humans make first contact, some sort of war happens. AFAIK, only Vulcans did not try to enslave/wipeout us. Well, may be Centurians too, but Minbari rectified it

a vicious, space-traveling horde has more chance of stopping at the asteriod belt than earth. and if they want to get rid of us, they'd probably pick a worthless asteriod and drop it down the gravity well. that is, if the're 'rational'. being particularly vicious is the only reason i can think of for them to attack us.