The best place to start is the beginning and as we could argue that point in and of itself I shall tell simply choose the day you went to Ponyville as an acceptable starting point and only go further back to the past as is necessary for the sake of argument.
Now you had concerns about the return of Nightmare Moon, as you had every right to be, but when you brought this point up with your precious instructor Celestia she merely told you not to worry and sent you to make some friends. We both know why she sent you to do so but would 'Honesty' from your teacher prevent you from making friends, I doubt it.
In fact throwing you into a situation where a god like Alicorn princess wanting to steal the sunlight allowing for plant growth and eventually killing off all life save for the Diamond-dogs, Dragons and my empire that can survive on crystals, without any warning wasn't very kind now was it?
You had to go through the most dangerous forest in Equestria chasing a rumor that could have been confirmed to exist by your mentor but was opted to remain a secret, and in the end you found and used these Elements of Harmony to purify Nightmare Moon after she tried to repeat her crime after failing 1000 years prior to her sister, a tad light on the punishment when you consider the following.
Discord, the spirit of Disharmony and chaos had revived and did just what he was born and destined to do, not so unlike yourself. After he refused to stop his harmless pranks at your request you and the other element bearers turned him to stone, for following his calling.
Then there is Queen Chrysalis who went to Canterlot to find food for her kind. A food source mind you that could be given with no true harm done to the giver. While I understand that you could not simply allow an invasion to take place, I know for a fact that no attempt at diplomacy was attempted and you simply resorted to expelling her and her kind from the capitol by force. Her methods were wrong but that does not make yours right. Your actions left the changelings forsaken for trying to simply live. It's not like they eat you as a wolf does.
Then there was me and my empire. I was kicked out of my keep and when I attempted to regain control of my kingdom you attempted to destroy me. And for what reason was this done for I do not recall being accused of any crime nor attending any trial. Is the death sentence something given out so easily by your princesses?
If we look to the past for answers we see that when the moon needed lifting, instead of returning to a unicorn council she chose to do it herself. With the sun she controls the harvests and with the moon she has the seas. Why would it be a good idea for the ruling body to have such control over resources which almost all living rely on? While it can be used to prevent wars among neighboring nations it also could be used to blackmail them into following her whims.
Now consider me and my empire which care not for the current state of the sun or moon. Would I not seem like a threat to her? To avoid conflict my kingdom was hidden away for quite some time until I could be dealt with.
But enough about her, what about her sister? She strolls through the minds of the sleeping without a care in the world. Such an invasion of privacy is quite immoral by my standards. Then there is the invader of my home, Cadence. She forces love on others without fear of consequence.
When you attempted that as a unicorn you were lectured for the act, when the filly's without a cutie mark did it they were punished, when Cadence does it she is praised. Does that seem fair? You see it is a way to show that only Alicorn princesses my manipulate the minds of the subjects.
My subjects might not have always been happy but I allowed them to chose the state of their heart. Now happiness is forced on them like the chains I was accused of to keep the peace to a silent tyrant. Did you see any sign of the kind of cruelty I was accused of? If it was to the scale of the accusations then some signs would remain.
Unlike your ruler I favor the health of my subjects and not a single pony died during my reign, well over 1,000 years. Why would ponies be allowed to die when I have proved that death can be prevented? Simple, another perk only allowed to Alicorns.
Now lets assume the things I have been accused of are indeed true. How is the ruler of another nation in any position to have a say in how I rule. Let alone forcing her moral principles on another culture which simply should never be done as crushing a culture is an act done to impose rule over slaves.
If it is not the culture but me personally she thought to be immoral, well that is unfortunate because I had done nothing unlawful. Only society may punish immorality by shunning the individual, law is left to deal with crimes. And my laws are not hers and vice versa.
While we are on the subject of morals, the elements that form the foundation for Equestrian ethics are far from perfect. By helping another in an act of kindness you rob them of a challenge to overcome. Correct me if I am wrong, but theft is still considered wrong. By generously giving food to the needy you create dependence in them for your gifts. Honesty forbids the hiding of truth and secrets of friends must be revealed else you would not be, telling the truth. You can be loyal but to who do your loyalties lie, for helping Luna turned Nightmare for the sake of loyalty is folly. Bullies can get laughter out of harming others. Then there is magic whose constant use prevents progress of technology, forever keeping the other races at a disadvantage.
With all that off my chest I wish you a long and peaceful rein of upstanding ethics and harmony.
Author's Note
I don't like the last line but it needed some sort of end and "Long live the Queen" would have been a tad cliche. Another potential ending was "Oh, before I go I would like to know, have you stopped using your magic to torture foals? / Wha- no. I-/ Ah, another benevolent ruler I see." and he would leave. But that would really kill the tone set here.
Hope you liked it.