Maybe you are good today, but in the future you might start to be swayed by changing incentives or situations due to forces such as "absolutely power corrupts absolutely".
Or maybe you manage to always be good, but--as humans have fixed life spans--eventually retire or die or simply move on and are replaced by someone who is less good than you are.
Or maybe you are good but the power you manage to concentrate gets stolen by someone (in the digital world, maybe you get hacked) and used without your permission to do bad things.
Or maybe you want to be good, but your power is seen as an asset for something external--such as a government--and you end up being required to do bad things that make you sad.
We see all of these issues play out constantly with large tech companies, with control techniques such as curated application markets getting abused as anti-competitive measures, or getting regulated by authoritarian governments as a tool for their regime.
In 2017, I gave a talk at Mozilla Privacy Lab that looked at many of these issues, citing tons of situations--every slide is a screenshot of a news source, as somehow people always want to believe these situations are far-fetched--where having control has gone badly: