Main Entry: ag·gres·sion
Pronunciation: &-'gre-sh&n
Function: noun
Etymology: Latin aggression-, aggressio attack, from aggredi to attack, from ad- + gradi to step, go -- more at GRADE
1 : a forceful action or procedure (as an unprovoked attack) especially when intended to dominate or master
2 : the practice of making attacks or encroachments; especially : unprovoked violation by one country of the territorial integrity of another
3 : hostile, injurious, or destructive behavior or outlook especially when caused by frustration
Seeing as how words such as "forceful", "unprovoked", and "hostile" are part of the definition of aggression, I don't think you can really argue that it doesn't imply non-consent. If someone is whipping me because I ask, that person is not "forceful", "unprovoked", or even "hostile" because I want it done.