The reason why so many people call Letty BPD and evil is because they want somebody they can hate. It's a reality TV show at the end of the day, and people want to see the person they perceive as "evil" suffer. Letty got thrown into that box for a few reasons. She's a chick with a sketchy past who pushed herself in certain challenges. She tried to sabotage her competition early on and was punished for it. It's much easier for a person to look at that and think "Wow, what a fucking BPD bitch, I ain't no simp, she's pure fucking evil." Rather than "Wow, this person is trying really hard to win this show, to the point where she's dealing with a constant shit storm because of it. That's admirable."