First of all it needs to be established that all people that Walt kills throughout the show are other "players": Gus, Lydia, Mike, Gus's guys in the prison, Krazy 8, the nazis, Gus's goons in the lab..
They are all hard-boiled criminals themselves and/or murderers who got freely into the "game". I just can't see Walt being being a monster for taking these other soldiers in the game out. They would have no qualms doing to the same to Walt (actually, except for the guys in the prison, all of them tried to kill Walt before he kills them!). And frankly, Mike deserved getting shot for his trash-talk; blaming Walt for the falling out with Gus, when in fact it was Jesse who caused it.
Grey areas:
Not helping Jane: Jane actually got into the game herself and became almost a legitimate target by blackmailing Walt. Remember that she told to Walt right in the face she might continue to blackmail him in the future! If you're threatening a drug dealer and meth-cook to expose him to the cops, don't be surprised that he refuses to save your damn life. If she told the same thing to Krazy 8, Gus or Lydia, she would have ended up with a bullet in the head the next day.
Furthermore it's also very clear that Walt's decision not to help her was greatly influenced by his love for Jesse. He rightly feared that they both would end up death with all this money.
Gale: Entirely Jesse's fault. He couldn't constrain himself and had to go against Gus' "employees". That's the catalyst that set all the bad things for Walt and Jesse in motion and destroyed the relationship with Gus. Remember that Gus and Mike wanted to kill Jesse foremost after this. The reason Walt was able to call Jesse in the first place and command him to kill Gail was because Mike gave him the phone after Walt promised him to turn Jesse in! If he would served them Jesse on the silver plate, there's a chance they would keep Walt alive in return.
If Jesse had not killed Gail, Walt would have died on the spot and Jesse's fate would be sealed as well. Gus had tons of connections and he would have found him eventually and bury him alive.
Brock: Entirely Jesse's fault and he had no moral high ground to be pissed off about it in the first place. I've recently rewatched Season 3 and 4 and Pinkman became a traitor in S4 already. Walt saved his life multiple times by that point (rescued him from the drug house, put him in rehab, killed Gus' dealers and handled Gail) and Jesse thanked him by getting enamored by Gus throughout the whole season.
Gus's plan was to divide Walt and Jesse and it worked wonderfully. I've read in this forum that Walt "manipulated and abused Jesse" - HELLO? Have we watched the same show?! Watch season 4 again! Since Walt saved Jesse from the drug house, he was like a surrogate father for him. The only fault was not going go-karting with him (big fucking deal). The only ones who manipulated Jesse by this point were Gus and Mike. They staged the assault on Jesse's first assignment and sweet-talked him against Walt to ultimately get the OK to kill Walt. And I doubt Gus would have kept Jesse, the junkie, for too long after this - he would have replaced him as soon as the next Gale would arrive, given Gus' stance towards drug abusers.
Jesse withheld information towards Walt in S4 throughout (not telling him about the SMSes Gus and Mike were sending him) and behaved like a complete ass towards Walt, and why? Because Walt was telling him the fucking true about Gus - that it's a plan to divide them, that the attack on Mike and Jesse was probably staged given how it played out.that Gus was doing all this just for show to drive a wedge between them and Jesse was to stupid to see that. And Jesse always pulled a tantrum after hearing the (logical) truth. Like a damn disgraceful bitch.
Every time Walt was telling him the fucking obvious facts, Jesse flipped out and even beat up Walt, his multiple-times life saver!
Walt was even ready to commit pretty much suicide for Jesse by taking a gun and storming Gus's chicken restaurant to find out what happened to him (Season 4, Episode 5). He left a "fare well"-message on Skyler's answering machine when he did that!
And where was Jesse's morality and love for children when he became in love with Gus? In opposite to Walt, Gus has not only poisoned a child, Gus ordered to kill children outright and used them regularly in his drug biz. It's very obvious that these two drug dealers killed Tomas on Gus' order, because:
1. They feared Gus and obeyed him.
2. Gus himself spoke very favorably of them. So he trusted them.
3. From the appearance of it, these two guys were not deranged meth-heads
4. If they really used children without knowledge of Gus, and if they really killed Tomas without Gus's consent and knowledge, despite Gus's lip service that children should be taboo from now on at the meeting with Walt and Jesse, why is he so mad that these two were killed? He should be thankful these unreliable and disloyal druggies were out of the picture - but no, he was so mad that he was willing to kill Walt for them, his elite-meth-cook! That shows that these guys followed Gus's orders to the letter.
So yea, Gus is a child killer, and Jesse didn't give a flying fuck one month later (probably because Gus is so cool, "Terminator-style" and all, which impressed Pinkman).
Walt was a master chemist and the Lily-Of-The-Valley poison is usually not deadly. Still: what he did to Brock is very controversial, but the situation with Gus was becoming so life-threatening to him only due Jesse's actions prior and Jesse continued to backstab him all the time in favor of the child-killer Gus. The Brock-plan arose out of an extreme emergency situation - Gus threatened to kill Walt's family and given Gus' connections, there might be even a mole in the DEA.
I could have understood it if any other character would despise Walt for what he did with Brock, but not Jesse. Jesse lost his "children above all" high moral ground when he colluded with Gus and he had no right whatsoever to betray Walt in Season 5. And let's not forget that by burning Walt's house down, he could have hurt children. All the things Pinkman was mad for at Walt, - Walt did all these things to save Jesse in the first place.
Pinkman is hypocritical traitor scum without any honor and gratitude. he deserved far more than what he got in that Nazi-dungeon.
I wonder whether there would have been so many Jesse fans if he would not have been a good-looking young man.