You can have good dictators, even if they are rare.
Hard disagree there.
But it really depends on what you value as good and bad.
For instance, if you think that people have an inherent right to have a say in how they are governed, then a dictatorship can never be good because it infringes on that right in the most serious of ways.
If you think a stable and sustainable system of government that will last beyond the life of a few leaders is important, then dictatorship is not a good system, because one good dictator creates no guarantee that the next dictator will be good, and establishing a system of dictatorship affords a bad dictator that much more power to ruin lives.