So they called him a monster. Well, at least he could take some satisfaction in knowing that he was a Monster of their own creation. With a capital 'M', bloodstained cloak, an unnerving smile and everything. He wasn't quite human either, which was just the icing on the cake.
The doctrines of a shinobi- as Kisame was taught them as a child- were that you did not (do not) fear death. Death happens. In fact, death is expected. Welcomed. Discouraged, of course, but hardly something to be controlled by. See, that's the difference between a person and a ninja. Most people are kept in check by their paralyzing fear of the great beyond, but a willingness to die for your cause... Ah, that's what sets a man free.
Or so they teach in Mist Village. Without any thought, really, for the psychological ramifications this might have on their children. They way Kisame saw it (and still sees it- probably will always see it), if death is a non-issue, then why not kill as many people as you'd like? Not like they're going anywhere you won't go eventually anyways, so you might as well have some fun while you're at it.
Reasoning which most people would call downright psychopathic. Kisame has never really had any excuse for this. 'The shark clan seemed like a good idea at the time' he'd chuckle, but then again biology offers no explaination. Zabuza went wrong as well, after all, so perhaps Mist just needs to sit down and re-evaluate their damn educational system until they find a viable method to stop producing psychopaths.
But since they didn't look to be doing that anytime within the next millenia, Kisame already was a psychopath (a Monster, as disussed earlier) so the Akatsuki seemed like the next logical step. Mayhem and chaos and murder- but with a greater purpose and a snappy red and black ensemble to go along with it. Besides, what with Zetsu being a dissascoiative plant man and Sasori being somewhat schizoid and, oh, Orochimaru's so twitchy he must be paranoid... Well, Kisame thought to himself ruefully, I must regretfully inform myself that I am the sanest one here.
And of course, the Uchiha boy, who was quite possibly the most dangerous of them all. Unless he wasn't, but either way Itachi wasn't talking so no would ever be the wiser.
"You're not funny." was the first thing Itachi ever said to him.
"I wasn't trying to be." Kisame answered truthfully. And grinned. Itachi narrowed his eyes slightly, and that was that.