There is a reason to fight them: layout. The battle is not developers vs users, its designers vs users. Designers want everything to look exactly like their vision (understandably), and that means things like bits of text fitting in exactly the right dimensions and placement. Once you let users resize things on a whim, that goes out the window, because most likely everything will look completely wrong.

It also opens the door for dead simple ad blocking that can't be stopped, and business owners will never stand for that. The purpose that the web has been bent to in the last 15 years is simply not compatible with user styles.