A musician should know how to read music. If you know how to read tab, you know how to play a piece of music on one particular place on the guitar neck, in the exact same way another musician envisioned it. If you can read music, you know how to play that piece of music in several places on the guitar neck. Plus, you have very little credibility with other musicians, (horn players, piano players, etc...) who know how to read music.

A guitar player saying that he or she doesn't want to learn how to read music is like a guitar player saying "I don't want to fret notes with my pinky finger." Tecnically, the guitar can still be played, but why limit yourself to such an extent?