It is hard for many viewers to like Kate. She was in the middle of most things, but never a critical factor in any outcome. She lived a miserable life. And, on the island, she found company with other miserable souls who had personal issues that ground them to a halt. Misery loves company. That is the Kate Austen story.
We saw a feisty young tomboy manipulate her young male friends into criminal activity and trouble. We saw her twist logic to justify what she wanted to do. She learned that her real father was the abusive step dad, Wayne. She decided to make things right in her own mind by taking out an insurance policy and blowing up the house and her biological father. (Never mind the subsequent factual farce of the story line of Kate's legal issues). Even on the run, she got her "boyfriend" to "rob" a bank just to get back a toy airplane from a safety deposit box. Once she got what she wanted, she killed him. Every time she was on the verge of happiness, she panicked and fled (such as her marriage to the Florida police officer, who apparently never Googled her background check before his vows).
So we have the foundation of this character summarized as follows:
1. Extroverted but aggressive child with anti-social tendencies.
2. Lashing out at parents for lack of attention or authoritative structure in her daily life.
3. Ability to use charm, guile and flirtation to get her way with weaker minded men.
4. Inherit ability to think on the run when in trouble.
5. Extremely lucky at times to accomplish her Houdini like escapes from the law.
6. The cold blooded killer instinct to eliminate unwanted things in her life.
Kate was clearly a troubled young woman. In her background, we don't have any strong evidence that she made lasting or close friends. She may have been the center of attention at school, but she was too hot to handle by her classmates. Her mother worked extra jobs to make ends meet so Kate was without maternal moral guidance. She had a free range childhood, mostly out on her own testing the boundaries of community standards.
She did not seem the type to want the spotlight of fame or fortune. She may have found Iowa boring, but even as the O6 media celebrity, she shied away from the cameras to become a suburban mother hermit. So, it was out of character for Kate to turn her moral attitude back to do an 180 degree turn to return to the island (but some remark that this was Kate's way of ending her responsibility for caring for Aaron.) Going back to the island was either a thrill ride escape plan or a death wish.
If the island was a place for redemption, then Kate would have been a leading candidate for change. She was an arsonist, murderer, liar, cheater, bank robber, adulterer, and selfish. The closest characters she gravitated towards on the island were Sawyer, a like minded criminal, and Jack, who had deep seeded personal self-esteem and father issues. In their own ways, both Sawyer and Jack led miserable lives even though they were successful in their professions. Kate was successful in nothing.
On the island, she had an intimate relationship with Sawyer, which may or may not have been a means of lashing out against Jack. Her relationship with Sawyer would sour and cool off. Off the island, she had an intimate relationship with Jack, which may or may not have been a means of lashing back against Sawyer who left her on the helicopter during the rescue. Her relationship with Jack would also turn sour and cool off, even upon the return to the island.
She became even more miserable on her island (1977 flash return) when she found that Sawyer had "moved on" with Juliet in Dharma bliss. With Dharma, Kate was a lowly nobody. She was frustrated that Jack gave in and gave up - - - no more leadership, no more wild plans or adventures, no more excitement. So if Kate wanted to get an island adrenaline rush, Jack was not going to be her partner in crime.
So even if Kate was plotting in her twisted logic mind that returning to the island was a means of punishing Jack and taking back Sawyer into her arms, she terribly miscalculated both her wiles and Sawyer's true feelings. Sawyer was suddenly happy being a normal guy with a normal job with a stable home life. He was stale plain vanilla, which must have startled Kate. When Jack went church mouse janitor on her, she was effectively left to be miserable alone.
If LOST was the examination of the loneliness in human lives, then what is the turning point that make true change happen? At the moment of resolution, with the defeat of Flocke, Kate had a choice on the cliffside - - - stay with wounded Jack or escape the island with Sawyer. She chose the latter under the guise that she "needed" to get Claire home to Aaron (but at that moment she did not know where Claire was or even if she was still alive.) Based on the objective evidence, the decision Kate made was to leave Jack behind and go back with Sawyer (to catch him on the emotional rebound so to speak). It speaks to her devious nature and her self-preservation mode against taking on the burden of responsibility for another person (in this case bleeding Jack). It was selfish of her to leave the island without him, especially if Jack was indeed her "soul mate."
Which is why many viewers were troubled by the fact that Kate wound up with Jack in the end. They had no sideways world connection - - - no relationship - - - no strong emotional bond. Any lingering memory of Kate by Jack would have been her leaving him to die (which could not command either respect or love).
In the Season 5 episode "Follow the Leader," the time skipping O6 are captured by the Eloise led Others. Jack reveals to Kate that he means to reset their lives, having the
plane never crash and avoiding all the misery that's happened since. Kate adamantly states that it was not all misery, but does not elaborate. He responds that enough of it was.When Daniel is killed, Jack takes up his plan to reset the island. Jack tells Kate that he wants to erase their past because he can't let her go. That admission seems to go against all the character traits of Jack; how can he still pine for her when he left her knowing her heart was given to someone else?
If we view the entire series merely from the perspective (or eyes) of Kate, we see despite all the tangents, continuity errors, bizarre premises and story line dead ends, Kate winds up happy if not content with Jack. She winds up in the afterlife setting a free person, never captured, never convicted, never jailed, never burdened with raising another's child, never accepting responsibility or accountability for her actions. Everything just falls into place: like a perfect dream.
So that could be the case that the series was really Kate's dream. She got away with everything and still got her reward in the end.