No. It is not the expectation given by the game text. It is the expectation given by your fellow players.
I would note that the Assault option's text explicitly says:
(Emphasis mine.)
Find me quotes in the game text and wiki that support this with more than vague allusions to attacking people, and I will reconsider my position.
As it stands, though, I believe you have simply been misled by the many people playing the game who want Infiltrators to be secret shadow ninja assassin killerz.
I have already added a line to the text an infil sees when successfully assaulting a noble that clarifies that the noble does wake up and attempt to defend him/herself, and clarified in the Wiki that the only actual assassination infiltrators can do is of militia. Not nobles.
I stand corrected and guilty as charged. Thank you for enlightening me!
