She didn't shoot people because YouTube uses unethical business practices. She shot people because she was an unhinged individual with extremist views about lots of things. She saw YouTube's apathy as a personal conspiracy against her content.
Whether YouTube's business practices are ethical and whether it's okay to shoot YouTube employees because of it are two separate questions. You don't need to be an ISIS sympathiser to take issue with what the US military is doing overseas.
FWIW whether YouTube's business practices are "okay" strongly depends on your political ideology and cultural background. It seems Americans, especially on HN, tend to hold the opinion that conning people into making bad decisions is (to some degree) okay because it's the victim's fault for being naive and careless. I'm German and thus have grown up in a country with strong consumer protection laws -- YouTube's behavior strikes me as obviously nefarious, but I'm well aware this perception is not universal.
YouTube disavow their responsibility by deferring their decisions to "the algorithm" and surely you can't blame a machine. But the obvious truth is that they're in control of it and could change it -- even if it is too complicated to predict, nothing is forcing them to use it and they could still replace it with something more predictable but less "error-prone". Instead they chose not to, which means they are entirely responsible for the outcome.
This isn't unique to YouTube either. Plenty of tech companies try to hide behind a wall of maths to justify unethical behavior.
The world of television is full of stories of pilot episodes that get picked up, are a smash hit for a few seasons, but get cancelled. The producers of those shows didn't have right to shoot up ABC, NBC, or Fox and many just licked their wounds and tried again.