Note:This gonna be a long post. But read it all, it's interesting.
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I found this on tv tropes WMG page. I found this pretty interesting.
From TV Tropes:"This'll be a pretty long entry. I'm going to use Dr. Hare's Psychopathic Checklist to prove that both of the above characters are psychopaths. (David in particular - I had to stretch it a bit to make and Cassie Rachel fit.) Here we go:
• Glib and superficial charm: David is pretty nice and friendly when he wants to be, this is what keeps Rachel at all bearable, and Cassie uses it to get people to do what she wants
• Grandoise self-worth: David's is obvious. Rachel's is more subtle, but when reading The Weakness, it's shown that she thinks she's better than everyone else - until everything crashes down, that is. Cassie always feels that she is the "voice of morality" for the group, and without her they would delve into immoral tactics.
• Need for stimulation and proneness to boredom: David couldn't sit still in a barn for two minutes without crashing through a hotel window, and Rachel is shown to always be the first to go on any sort of mission, rushing everyone with minimal planning. Cassie doesn't show this as much, but it does show in her constantly working in the barn, to the point where her parents don't find it odd when she's out there late at night.
• Pathological lying: This one's a lot more justified in the others, at least in Rachel's sense - she has to lie to her parents in order to survive. David, however, lies all the time, and not for much of a reason. Cassie lies when she feel that it is "justified": see her letting Tom take the morphing cube, among other things.
• Conning and manipulativeness: David's plans often involve manipulating others, such as when he pretended to be Sandler. Rachel doesn't do this nearly as much, but she does sometimes use others, particularly Tobias. Cassie doesn't use it as often, but when she does, it's devastating (remember who came up with the plan to deal with David?).
• Lack of remorse or guilt: David feels no guilt for anything whatsoever, and Rachel only feels guilty when her actions seriously harm humans - never when the mildly harm them or when the victim isn't a human.
• Shallow effect: David has this in spades, constantly pretending to feel emotions that he doesn't have. Rachel is also shown to have no middle ground between extremes of feelings - either (very occasionally) feeling strongly about something, or feeling nothing at all. Cassie feels guilt at harming anything; until she convinces herself it's justified and then doesn't get concerned again until the evidence is staring her in the face (see #19, bit of Hork-Bajir in her teeth).
• Callousness and lack of empathy: David's is quite obvious, and Rachel is shown to frequently kill or hurt others and only occasionally feel guilt. For Cassie, see above.
• Parasitic lifestyle: David would be hopeless if he couldn't force others to notice him. He constantly needs things from others - the morphing cube, a place to stay, Saddler's body... all without contributing anything to the people he steals from. Even his ultimate plan involves this - he wanted to give the morphing power to other humans who would support him and help him do crime. Rachel also needs things from others, if only someone to kill, someone to kill for, and someone to love. Cassie needs others acting in morally ambiguous ways, and needs to be morally superior to anyone else, up to being willing to be a caterpillar forever rather than let Aftran have the moral high ground.
• Poor behavioral controls: Oh, lord. Rachel has no behavior control at all - she is frequently shown to be completely out of control of her violent emotions, threatening (inside her head) to kill people and seriously hurt them constantly (particularly in The Return). David is a bit better, but he still couldn't help do things that were stupid (such as break into that hotel room) for no reason at all. While this isn't as violence-centered for Cassie, she does generally act on emotional impulse, even more so than Rachel, from temporarily quitting the team in #19, to endangering herself for the Buffa-human in #39, and generally putting herself in danger for no good reason.
• Promiscuous sexual behavior: Irrelevant - this being a kids series, there were no opportunities for sex.
• Early behavioral problems: Also irrelevant - we have little information on either of their early childhoods. On the flip side, there is no basis of comparison from teenagers onward.
• Lack of realistic, long-term goals: David's long-term goals make no sense - who does he think will get on board with him to do pointless and destructive crime, even if he does give them morphing power? Not to mention that this would attract massive attention from the yeerks and would probably end with everybody dying. Rachel's and Cassie's is completely justified in that none of the Animorphs have long term goals, other than to stay alive. However, Cassie does have long-term ideals, just no clear plan of how to achieve them.
• Impulsivity: We saw when Rachel took over in The Weakness that Rachel has no natural ability to plan anything - she's just more likely to charge into battle and kill anything that moves. David's a bit better, but he was still destructive with no real purpose or long term goal behind it - it was more like, "Ooh! Animorphs! I hate those guys! Let's kill!" Cassie, on the other hand, will say "Let's follow directions from this whale," or "Sure, I'll be possessed by the spirit of a long-dead guerrilla fighter,".
• Irresponsibility: Rachel is shown in the later books to almost never be able to do what the Animorphs ask of her unless it involves killing - same goes for David. Cassie also does not take responsibility for her own actions, often saying that she acts on feelings, or whims, or hopes, but with little forethought and serious retrospective rationalization.
• Failure to accept responsibility for own actions: Rachel only very occasionally accepts responsibility for anything, and it generally only happens when it would be absolutely necessary for her to be at all human. David is even worse, never wanting to solve any of the problems he causes for the Animorphs. Cassie give up the morphing cube and refuses to take the blame for the problems caused by morph-capable Controllers.
• Many short-term marital relationships: Another irrelevant factor - both are too young to marry.
• Juvenile delinquency: It can be argued that the Animorphs are forced to break laws, but both Rachel and David do it more consistently and more pointlessly than anyone else.
• Revocation of conditional release: David is told off for his counterproductive actions in the first two books of the David trilogy, but that doesn't stop him from continuing to do these things. This brings about his ultimate fate. Rachel is never punished for anything that she does, but even on the rare occasion that she feels guilt over killing someone, she still remains to be enormously violent and dangerous.
• Criminal versatility: Both Rachel and David take part in breaking tons and tons of different laws - they can basically do anything they want."
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So, yeah. Rachel and David are indisputably psychopaths. David was probably written this way, but with Rachel, it may be debatable, and Cassie is definitely a case of YMMV. Either way, it makes for a more interesting - and more horrifying - read.
