If we redefine everything based on what 9 out of 10 people do, what will the 1 out of 10 do that are trying to communicate effectively using precise terminology that wait... no longer exists for the concept they're trying to convey.
If 9 out of 10 people use it a particular way, it has already been redefined. What we're talking about here is the difference between prescriptive and descriptive linguistics: definition-oriented vs. usage-oriented.
If you're telling prescriptivists to stop prescribing, aren't you being a prescriptivist for descriptivism?
Descriptivism lets language evolve. Prescriptivism (people trying to push it back) is part of that evolution. According to your principles, you should just accept it as the way the language evolves.
Prescriptivism provides the foundation for descriptivism's point of departure, and descriptivism provides for the evolution of language. They are part and parcel to each other.
This democratization of language isn't necessarily correct.
There's a reason why we don't declare the existence of God as truth just because a majority of the population believes it.
There's a reason why majority rules isn't always appropriate. It's because often the majority can be wrong. We won't redefine the answer to the Monty Hall problem just because 9/10 people get the wrong answer.
If we're constantly redefining words and meanings, then why have definitions at all?
The fallacy is named because one of the definitions for "beg" is "to evade," which is why "begging the question" can be recast as "evading the question" (although you do lose the subtle part about assuming the conclusion to prove the conclusion).
