Yeah, words aren’t determined by dictionary committees or English teachers. They are determined by people using and understanding them.
All languages (other than ones designed deliberately, like Esperanto, Klingon, and Tolkien’s elvish) started from the same root and diverged when populations reduced regular contact and all words and grammars were made up along the way.
It depends on why you want to avoid being wrong.
If it’s just about being a good person by your own standards, then I’d agree that you can follow a moral code that doesn’t line up with any community you’re a part of.
If you want to avoid your communities turning on you, which could mean anything from silent looks of disapproval, reduced willingness to cooperate with you, complete shunning/exile/boycott, being targeted for others’ immoral acts, or legal consequences, then it’s a good idea to at least be aware of the differences between your personal morality and that of those around you.
And even if it’s relatively safe to follow your own moral code today, that doesn’t mean it will still be tomorrow. Even for “sins” committed today.