Them are fighting words.

This is absolutely true. For example, there are no rules in English barring the use of split infinitives, ending sentences in prepositions, or beginning them with conjunctions. These were all created by individuals who didn't like them stylistically. These rules percolated around and eventually got picked up by grammar-nazi school marms who drilled it into their students as though it were fact.

Yes and no. Much of what is taught in schools and passed around between laypeople as the so-called rules is simply incorrect. However, linguistics is a field with many scholars, who, as the scientists they are, observe, experiment on, and model language. There are lots of theoretical debates, especially because linguistics as it stands now is a fairly young field, but that doesn’t mean misinformation is all there is.

Yes, because language has evolved (often in parallel) and is memetic. The whole thing is one big game of telephone. I believe this is why Stephen Wolfram is pushing to create a new form of language similar to maths that can be used to universally communicate anything. Because everything else is subject to history and context.