Gale should've been Jesse's first kill

Sure, Gale was a criminal, but he was a nonviolent one. Tucco, the rival dealers, and Krazy-88 were all violent men who were willing to kill others. In the case of Tucco, he was an outright psychopath who enjoyed inflicting harm on anyone, including his own friends. The rival dealers had a kid go out and shoot their competition. As for Krazy-88, he was polite, but he was still willing to kill Jesse and Walt before they captured him and he was still going to go through with the murder even after Walt briefly decided to let him go. They weren't nice people by any means and there was some element of self-defense in all of the kills.

Gale, on the other hand, was educated, nice, and seemed to only be involved with making meth for the science of it. He was an awkward and quirky guy but he wasn't anywhere close to being as bad as Tucco or Krazy-88. That doesn't excuse him being a part of a drug ring, but he didn't deserve getting shot in the face in cold blood.

I agree with you for the most part. Jesse's character did change a little after season one which made Gale's murder seem like it impacted him more than it should have considering he was not a stranger to these kind of things. I would credit that the producers originally had Jesse dieing off very early but were so impressed by the actor that they made him a core character.

However, I will argue that Jesse didn't have any interest in killing K-8 he wanted him dead sure because he knew that K-8 would def kill them if were to be freed. But I had always doubted he could actually go threw with it himself. He was extremely relieved after the coin flip. He was freaking out after he realized that the gas wasn't going to kill K-8. Had Walt not been involved he wouldn't have lasted very long he wouldn't have been able to kill K-8 and would have never been able to depose of the dead body. Police would have caught on to Jesse quickly, shoot the only reason he wasn't in jail to begin with was because he happened to be banging the neighbor woman while the DEA raided his operation that Walt witnessed.

About Tuco, Jesse was just trying to live he was sure he was seconds from death and even then he doesn't do anything that actually kills Tuco and stands down the second that Tuco is no longer a direct threat to his life. Tuco was adrenaline and self defense. While Gale was a guy that had never harmed Jesse and he killed him straight up. Big difference between the 2 situations. I would argue Gale was Jesse's first direct murder. Not only that but it was the first person Jesse killed that wasn't already trying to kill him directly.

I guess I relate this to Band of Brother where one of the characters is traumatized by killing an unarmed German. Even tho he had shot and killed dozens of soldiers before this it was the fact that he killed a man who directly posed no threat to him but knew he had to anyway. A person they killed who wasn't directly trying to kill them.

You raise some very valid points. But Tuco and Krazy-8 posed threats -- so it was a potential kill-or-be killed scenario. Gale-- although innocent-- posed a similar threat to Jesse and Walt. Once he possessed all of Walt's knowledge, it rendered walt and Jesse completely expendable. So Gale's murder was a tactical move that was just as logical as killing Tuco or Krazy-8.

I think one reason why Gale's murder affected Jesse more was that Jesse had taken a step towards sobriety, which leads to a lot of self-reflection and repentance. Staring at an innocent, unarmed person pleading for his life would have that kind of effect on anyone.

Gale was Jesse's first kill. Krazy-8 and Emilio were both killed by Walt; Tuco was killed by Hank; the rival dealers were killed by Walt. There's a lot of difference between completely hypothetically thinking about killing someone, wanting to kill someone and actually doing it and Jesse never actually crossed the line into direct killing until he shot Gale - who was someone he didn't even particularly want to kill anyway, it was just that he was convinced there was no other option.

Jesse is constantly characterised as someone being increasingly pulled out of his depth. He's like a little kid acting knowledgeable about stuff but it only really works on other little kids. He had various opportunities before the coin flip to deal with Krazy-8 himself and was visibly relieved when he got to deal with Emilio...despite saying minutes earlier that he wasn't good with dead bodies. So I don't really know where you're getting he'd kill the guy without hesitation. He couldn't even hurt Skank and Spooge when he was trying to get his money and meth back from them, despite actually being armed and in charge (for the most part) in that situation.
Jesse presents himself early in the series as being the streetwise partner to Walt's book-wise personality, but that results in him constantly getting into situations he's not prepared for. And no, to him going to the police would never really be an option because his survival instinct was too strong - going to the police at any point would have resulted in time behind bars and he knew that; it's not until he fully realises how far Walt's willing to drag him down that it ever becomes even a remote possibility. There's a strong implication that violence hardly ever even entered into his dealings until the start of the series. Really, until Gus' two dealers, it's debatable whether he even crosses from the hypothetical "we should kill this guy" to the legitimate mindset of actually wanting to be responsible for someone else's death.