Yeah, good point. He was actually much more aligned with the goals of his assassin, Gavrilo Princip, than Princip knew. Princip thought he was doing something that would help the Bosnian / Serb cause, but instead he killed someone who might have given the Bosnians / Serbs more autonomy.
The thing is, I’m sure that there are cases where political killing actually makes things better. Obviously, it often makes things worse. But, it must be true that sometimes it makes things better. The problem is, that there’s no alternative history you can consult to prove it. You can just speculate about what might have happened if that person had not been killed.
For a random example, take Carlos Castillo Armas. He was put in power in Guatemala thanks to a CIA-backed coup. The US was involved partially because the democratically elected president was thought to be under the influence of Russia. But, more importantly, he was doing things that were hurting the bottom line of American fruit companies. When he took power, he started doing dictator things: rounding up and killing opposition, shooting protesters, revoking civil liberties, etc.
Then, 3 years after he took power, he was assassinated by a bodyguard.
What happened after that was probably not good for Guatemala. There were 36 years of civil war, and a lot of unrest. On the other hand what if Armas had been able to consolidate power? Would decades of dictatorship have been better or worse?
Also, killing an established, truly evil dictator almost never results in a happy democracy. But, that’s probably because the dictator has destroyed all checks and balances, wrecked every institution that a working society needs, and eliminated anybody who might be a threat. So, if a dictator is killed, the result is often chaos, or another dictator taking over. But, if you eliminate someone who might have become a dictator, who’s to say that they really would have become one?
Predicting the future is hard, predicting the past is easy.