Disagree that being harmless is enough (in the serious unaligned takeover scenarios). You have to be valuable, or at least more costly to kill than the resources you will divert from the AI’s goals.
A god will not bother with killing ants.
Humans kill a LOT of ants. I personally try to kill any that come to my notice near me.
Bad environmental effects could kill humans. For example, AI starts to send millions of missiles to space and atmosphere will be polluted with their exhaust.