A word should be defined either by arbitrary authority, or by etymology, and ^not^ by common usage.

Good luck changing the rules of the English language. Words have been defined by usage rather than by arbitrary authority for centuries. The rules aren't about to change any time soon.

As for the word 'pedophile', if they were to be defined by an arbitrary authority the definition would still be "an adult who is sexually attracted to children'. That is the definition you will find in the vast majority of dictionaries, and it is a simplified version of what you will find in medical or psychiatric journals. The authoritative definition would still be the definition we currently have.