I don't get how Gale is evil though? He tries to have his bomb disabled alongside the tadpole. He reveals it to you when he's comfortable enough, and it is something that he could just hide if he is manipulative and evil. he also told you a story about how he defused a violent situation and save lives after seeing you resolve some conflicts. Most of his approvals come from you helping people out and select the benevolence option. I don't get much evil vibe from him. He also leaves your party if you side with the evil faction. What makes him evil exactly?
Gale's "evil" is rather subtle, and hence an excellent example of the different shades of evil featured in BG3.
I classify him as "manipulative evil" because his morality is most questionable when it comes to him pursuing his desires. He is 100% willing to jeopardize others or deny people their agency (by withholding facts) in the pursuit of his goals. He's far from a mustache twirling villain, and he's probably someone who'd genuinely wish you well if you didn't have something he wanted, or not in his way.
The first sign is obviously how he chose to reveal his secret to us. For a party whose entire reason for being together is to try to find a way to stay alive, the fact that he's a walking nuclear bomb is very important. I don't believe that Gale waited until he was comfortable to share his secret. He started hinting at his secret because he wanted to consume the artifacts that you gather. He strategically reveals it to us when he feels like he's disarmed you enough to guarantee the outcome he wants. He effectively manipulates the situation to deny the player agency - an educated choice up front.
We see another example of this during the tiefling party if you're romancing him, where Gale once again denies the player agency to go after what he wants. After the party, he'll reveal to you the full extent of his condition. If you had slept with him and get pissed off at him for not telling you about his explosive condition + past obsession with Mystra, he explains himself by saying that
he couldn't tell you because he'd lose his chance to sleep with you if you knew the truth. Lastly, the most damning evidence of this behavior is his backstory itself. Tampering with Netherese magic is exceptionally dangerous, and the fact that it is related to Karsus's Avatar makes it even worst. It takes a certain level of arrogance and sociopathy to deal with magic that dangerous, all to "win back" an ex. It's not that he's going out of his way to hurt other people, it's more that it seems like in his mind, he doesn't care what the effects or who it harms, if it can get him what he wants.
So sure, while Gale doesn't condone murdering an entire village of innocence, that's such a cartoonish-level of evil (especially when you consider that no one really gains much out of it) that I'm frankly glad BG3 isn't solely exploring. He's kind of the everyday, law-abiding citizen until that one time he manipulates and risks all of his friends lives to get something he wants.
On a more meta-level, we've heard Larian say that only the evil/neutral companions are in right now, and in Kevin Van Ord's stream he did mention that of all the companions, the one most leaning towards good is Wyll. This doesn't pin point Gale as evil, but it is why a lot of people (myself included), have read deeper into Gale's actions/story, beyond his facade of friendliness.
