Khashoggi wasn't a great guy. He is far from a saint.
That doesn't justify kidnapping, torturing, and killing (and subsequently killing participants).
Many of Putin's adversaries are far from saints, and Putin is probably one of the best things that happened to Russia (and by extension to global and regional stability) in many years. That doesn't mean that all the methods he employs are right, and doesn't justify them.
That being said, hypocrisy runs wide. Erdoğan is far from a saint, and doesn't treat dissidents that much better, nor is he an advocate of democracy or free press. Same can be said from many regimes around the world.
The problem in this case that doesn't allow the world to remain silent, is the way it was done, and the location where it was done.