They're clearly not.

At the same time, they may be propping up a tyrannical system. "Just following orders" is not a solid argument for your morality.

It's clearly a complicated mess. My personal hope is that we eventually learn the lesson that sufficiently influential social networks need to be subject to democratic oversight and a transparent judicial system. That will likely make them more expensive to run, but that's a price we have to pay for three sanity of our society.