While Caitlin has been on The Flash since the very first episode, Killer Frost slowly overtook her in popularity from the time her character was foreshadowed before she joined the team in season 3. Her edgy character and snarky attitude endeared her to some fans who enjoyed seeing the contrast between her and the other half of her personality.
However, the same edginess and snark that made some fans love Frost put others off as it resulted in two characters that were difficult to understand or relate with. Among the many opinions fans share on Reddit about Frost, her character, history, and contrast to Caitlin are prominent topics of discussion and the subject of many unpopular opinions.
She's A Poorly Written Character
After her introduction in season 3, it took a while for Frost and Caitlin to find a proper balance that allowed them to co-exist in peace. That search for balance resulted in two characters who weren't properly developed to stand out as separate individuals.
As Reddit user jdessy said, "Killer Frost is a poorly written character who was never fully developed." The poor development can be attributed to the struggle to give each character an identity while trying to maintain a middle ground where Frost and Caitlin could both fit in without going completely out of character. Now that they're two separate people thanks to their split in season 7, fans hope that Frost will get more development this time around.
She's Better As A Villain
Since she became part of Team Flash, Frost struggled with straddling the line between hero and villain. In season 3 when Caitlin was determined to get rid of her, she was at her most villainous, which Redditor riabe felt was when she was at her best and said "every other Killer Frost arc has been a major let down."
Caitlin's evolution to Frost was an interesting storyline because it was a twist on the classic good girl goes bad plot, which might explain why fans preferred her as a villain even though she wasn't as bad as the other villains on The Flash. Other story arcs involving Frost, like her taking the reigns in season 6 or her recent trial in season 7, haven't had as much of an impact and thus are less popular with the fans.
Her Split Personality Doesn't Make Sense
Before Caitlin and Frost split in season 7 and became two separate people, they shared a body and took turns being in control. Reddit user Slippery_Syzoth questioned the logic of ice powers causing Caitlin to develop a new personality and said, "the split personality concept was an interesting one at first," but now it doesn't seem to make much sense.
The concept absolved Caitlin of taking responsibility for the things Frost did in season 3 and mostly swept them under the rug until season 7. The redemption arc that the show tried to add in seasons 6 and 7 did make some improvement to the story and the two characters, but not in a way that satisfied fans.
Scaring Killer Frost Out Is Weird
While Caitlin and Frost were still one, Frost would only come out whenever Caitlin was scared or in danger. It became a running gag on the show for the other members of Team Flash to scare Frost out whenever they needed her, but some fans like Reddit user sleepyotter92 thought it was an odd practice and said, "the whole scaring Caitlin to get Frost out is the most ridiculous thing ever."
The logic behind the practice was understandable, but because it happened several times and was mostly played for laughs, fans stopped seeing it as something serious and viewed it as a joke instead.
Caitlin & Frost Are A Mess
Both Caitlin and Frost experienced trauma in their lives, especially with their father, Thomas Snow, who turned out to be Icicle—an evil man with ice powers. So, turning her into a completely different person on account of trauma that she experienced too was a little confusing for fans.
Since neither Caitlin nor Frost are all the way good or all the way bad, the combination is a character that's difficult to understand as Reddit user NathanNjose said, "Caitlin Snow/Killer Frost is a complete mess of a character." Most fans complain that the writers of the show failed to commit to making Caitlin all the way evil and giving her a proper redemption arc, which would have been better for the story, and as a result, Caitlin and Frost's personalities weren't developed properly.
The Trial Against Frost Didn't Make Sense
While discussing the trial against Frost in season 7, some fans argued that the prosecution's arguments against her didn't make sense at all. User Tanweer-Ayman went on to comment that the whole case was contrived because "they needed to take away Killer Frost from the show as it was too much work to handle 2 characters played by one actress."
The prosecution's argument might have holes in it, but the trial was necessary as Frost's previous crimes dating back to season 3 hadn't been addressed. Unfortunately, although The Flash finally followed through on bringing Frost to justice for her crimes, the execution didn't go very well or in a way that satisfied the fans as user Batsincvic888 argued.
Shouldn't Have Shelved Caitlin For Frost
In a bid to give Frost room to grow as a character, the show sacrificed Caitlin's development instead. This was especially evident in season 6 when one of the major plots was Frost wanting to live a life outside of protecting Caitlin. It led to the running gag of Frost having inside jokes with Ralph and Cisco, and Caitlin feeling left out. So, rather than fix Frost's personality problem, it made Caitlin's personality worse.
Some fans, like jdessy on Reddit made the argument that the characterization issues would have been solved by eliminating the dual personalities and making Caitlin and Frost into one person with all the best parts of each other. Especially since the Killer part of Killer Frost was eventually permanently removed, making Frost simply a snarkier version of Caitlin with powers.
She's Not Likable
When comparing Caitlin and Frost, most fans prefer Frost because she's snarky and funny whereas Caitlin is a lot more reserved by comparison. One Reddit user, Slippery_Syzoth, shared an unpopular opinion that stated the opposite and said, "Killer Frost comes across as edgy and unlikable."
Her snarkiness can be a little hard to get used to as even some of the characters on the show found her to be too mean, like Kamilla after Frost made fun of her art. Her character did improve a little over the seasons, especially after the split from Caitlin and fans hope that she'll have a meaningful redemption arc this time around. Based on some underrated moments on The Flash and her actions in season 7, as well as her commitment to seeing the trial through, it seems she's making great strides towards becoming a better person.