Why do people act like violence is only bad and never justified.

My coworker and I were watching transformers one and I said megatron was mostly right in the movie and that optimus was highly idealistic and he disagreed and we talked it over. Later on I looked to see if people agreed with me or him more so I looked it up on tik tok and people were talking about how good Optimus was and how megatron killing sentinel prime makes him just as bad. Sentinal prime killed some of the best people in the world, betrayed his entire species for his own self gain, then enslaves them, took nearly everyones powers, and 10,000 other things. Sentinal deserved it. Allowing him and his co-conspirators to continue to live and just be like well we will tell them not to do that or they were just taking orders. Just taking orders is no excuse and allowing sentinal and his followers to live is only enabling him because even if you imprison him and his followers any given chance they will betray the transformers again. Obviously this does not apply to people who didn’t know what was happening. I disagree with how extreme megatron got at the end but much of what he said was absolutely justified