So is the equation innocent blood demands the revenge of innocent blood.
Yes there has been atrocities by the west, there has been exploitation, so the revenge must be some form of atrocities and exploitation? Is that the new equation, because an Airstrike created collateral damage the natural outcome of it must be people who had nothing to do with the airstrike being mowed down?
Let's recall another set of atrocities and exploitation, remember Jalianwala baag, and General Michael O'Dwyer who mowed down more than 1000 people brutally ... In response Late Uddham Singh did not go to London and start butchering random people, he could have, by what you have stated, his response would be the natural outcome, but he assassinated General Michael O'Dwyer.
His last words were:
"I did it because I had a grudge against him. He deserved it. He was the real culprit. He wanted to crush the spirit of my people, so I have crushed him. For full 21 years, I have been trying to wreak vengeance. I am happy that I have done the job. I am not scared of death. I am dying for my country. I have seen my people starving in India under the British rule. I have protested against this, it was my duty. What a greater honour could be bestowed on me than death for the sake of my motherland?"
These were the words of a Hero, One who conscientiously avenged for the pride and spirit of his people, did not hold a grudge against the british commoners or any other officers who were following orders, and then stood his trial to die a proud man. And that is a stark difference between heroes and terrorists.
You ask what is terrorism, the classical defination might be fear and intimidation for political goals, but this is not just fear and intimidation, this literally is subversion and cowardice of one's generosity to attack behind in the soft spots. these are no warriors avenging anything, these are just scums, pure scums.