Jessie did force Walt to kill Gus's boys though
Jesse was going after them because they killed Andrea's little brother.
They killed Andrea's little brother because they used him to kill Combo and he was a loose end after Gus told them no more kids.
They killed Combo because Walt forced them to sell on the competition's territory.
Walt was presented with a job opportunity that would've given him a lot of money and access to the best health care in the world. He turned it down to sell drugs and work with criminals. You can't claim that poisoning a 9 year old was for the greater good of protecting your family when you voluntarily made the decision to become a drug dealer and work with dangerous people.