After all that happened, I feel that my post won't contribute much, but what the frick... might as well try.
Truth to be told, I found Cait Sith out of place the first time I played and not because of his nature (stuffed robot), but because of his function. Fortune teller??? Wat???? It was something unusual, to say the least. Now, this isn't a bad thing per se, but it did leave me with a "WTF?" face for some time.
Then, there was the excuse to join the party: "I need to see how my prediction comes true!" and... he is allowed to join. WAT????? My main issue with that was that it made the members of the group look idiots who are unable to put priorities. Here we are, looking for a psycho killer that did atrocities and has immense power, having the most powerful company on our heels, a company that in fact created said psycho and has no problem killing others to reach its goals and... we take along this thing like that? WAT????????????
At that time, I had no idea that he was a spy from Shin-Ra, and I facepalmed at that reason. He seemed so random, as if the writers had come up with him the last moment, just for some filler lulz. I didn't appreciate it.
Then, the moment of his betrayal came and I changed my mind. I was finding the story stalled at that point and Cait Sith made the plot moving again. I also vaguely remembered a Shin-Ra member that seemed to care about the world a little bit more than the others, and I started suspecting. Then, his sacrifice came and even though he was a robot, I couldn't help but feel emotionally touched, if only a little. It was then when I realized that Cait Sith was providing something necessary: comic relief (apart from the plot elements). And it was funny for me, because I always adore the comic relief characters in the stories I read and I value humor more than most story elements. Cait was just way too obvious and in-your-face comic relief, I guess.
His introduction might have been goofy, I still believe that, but in the story he became a integral member.
As for his existence ruining the sci-fi world... wat? Here we have aliens that are used to make super soldiers, a river that includes dead people... we're gonna get stuck on that??
And to be mean: DLPB reminds me the same people who complain about Puck in the Berserk manga. *rolls eyes*