I think that aikido in the US accents less on overt aggression than the very Americanized forms of other martial arts. My first sensei (Shorin Ryu Karate) was a very mellow, non aggressive, simple man. He did not encourage his students to take on an aggressive stance, nor shout out their kiais, nor strike pre-emptively. He wasn't the stereotypical arrogant 'Cobra-Kai' MA instructor, but there are less out there than many assume. It's a stereotype I think.
Sure, there are MA organizations which help perpetuate this stereotype.
However, I think that the media prefers to accent on these stereotypes.
Okay, so humility can be another story. I have certainly read some pretty arrogant and flippant commentary on this and other Aikido websites, and I confess I have faltered myself. I think overall if the dojo mindset encourages 'harmony' in their 'do' then there is more of a feel of passivity which can seem like humility. However, how many times has an aikidoka thought to themselves 'I can do x technique better than so and so.' or 'I think this visiting sempai got their rank before they should've.' or even 'X style of aikido really isn't very effective, mine is better.'
I must admit I may have thought one or two of the above things at one time or another, I'm working on it though. It's that whole masakatsu agatsu idea. I haven't reached victory yet.
just my 2