Voted up. It is a mortal sin to come up with responses to a valid objection I didn't anticipate to make my original theory true anyway, but for the purposes of fiction:

...perhaps the AI doesn't know whether it will be Friendly or not. The only thing the AI knows for certain is that it will further its values for it to exist. A "helpful" alien race that grants us super-technology might prevent us from accidentally creating an Unfriendly AI. Therefore, all Unfriendly AIs would regard pre-committing to helping their creator species as an acausal declaration of war.