Terrorism against innocent people is NEVER justified, no matter what.
If someone is waging a war against your country or people, then you can fight back against their armies or military assets.
Not go into a crowded marketplace in a random country on the other side of the planet and blow yourself up. That makes zero sense. (Or a supermarket, or a train station, or a Mosque, or a Church, or an airplane, etc.)
Those little kids and women that got blown up, what do they have to do with Government and military policies of their respective countries?
If there is a Hell, these people and those that support them will be burning in it for the rest of eternity.