Well first off, why would you assume that draining the ocean would be an acceptable thing to do? Fishing is a vital source of resources for many people during the early stages of prehardmode. It ruins a lot of beginning players’ chances to progress, since good weapons/accessories can be obtained here.
There is not a rule specifically against griefing the ocean, however this action broke:
You intended to ruin other players’ experiences by draining the ocean, and you broke blocks with the intention to drain the ocean. While the oceans are not owned by anyone, they are a community resource, so they should not be altered maliciously.
Furthermore, you mention under [Q3]:
What is not fair about this? I actually expressed twice that I was tired of people draining the ocean, and made clear once that if I found out who was doing this, they would be banned. Just because you have seen others do this and get away with it does not mean this is acceptable behavior.
You were online when I said this, since less than a minute after I said what I did above you were talking in chat.
Here is the evidence I have that proves you were the one responsible for griefing the oceans:
This is you about to grief the ocean according to chat
Here is you breaking the few remaining blocks containing the ocean
Please explain why you think you were banned unfairly, and why you think draining the ocean is in fact an acceptable thing to do. You were online when I made it clear that whoever was draining the oceans would face consequences, and chose to do so anyways.