What if Blackbeard had used the chalice before MC got there? What if these pirates were actually a bit more capable?
No harm came out of anything that Pearl did because the MC was there to fix things. It's not a good argument, because you could say that no harm resulted from anything Selena did either because the MC put things right.
The whole "daddy made me do it" is just too easy of an excuse. I can honestly understand that Pearl betrays the MC to keep Mira safe. What I don't understand is that Pearl later boards the ship to attack Mira, saying that their father ordered her to get rid of her. That she attacked to chase Mira off... What was her plan? "Hey sis, I beat you, so now you have to sail away and never come back"? As if that would've worked with a firecracker like Mira.
That the MC doesn't even have stern words for her is ridiculous, specially when the story gave us plenty of information on how the MC views betrayal, and how a dark-path MC would handle it.
You mean Kira, right?
According to Pearl she did not attack Kira to kill, she did it to chase her away to save her from her father's wrath. Also, even if they feel close to MC, they'd choose, both of them, their own twin over MC everyday. So that also made sense. We honestly don't know how powerful was Blackbeard, MC dealt with him with ease. (Probably because his lack of potential to become an LI) But Pearl feared him, Kira too. So if he threatened Pearl to kill Kira, that really make sense.
If you are comparing that to Selena. It really is not. One of them puts their so-called friends in active danger. Even after she denies it, she is very well aware Taron was going to kill both MC and Eliza. That's active betrayal. Not even counting she was part of the ambush that Eliza got kidnapped and it was her who lured Eliza away from MC for the ambush. On top of that, she gloated at the cell. She even mentioned how not either MC or Eliza survive the situation. I am still salty that MC can't kill her and let her sister go. She deserved the worst.
In Pearl's situation, she took a chalice to save her own twin sister. It was just another trinket a pirate stole, nothing more. Yes, MC do believe it could help someone she does not know, a person she never met. She did not know if the chalice would work, even if it works would Eliza accepts it, Eliza (a person she only know as MC's friend, if Pearl even know that much) was not going to die, if Eliza did not get the chalice there could be another way to help her too. Her sister was in greater danger than somebody she did not know.
Also, another huge difference, Pearl did not follow through the plan, she helped MC and Kira. Selena did followed through the entire plan, gave MC and Eliza on a silver platter. She was not regretting when MC caught her, she would do all over again for under the same circumstances while Pearl was regretting and she noticed she could have choose another path.