I respectfully disagree with Notes.
I don't think every musician should learn how to read standard notation NOR know basic music theory.
I agree that there are SOME musicians who, possibly because they've never been around music much, or never grew up with music, SHOULD do both. I've played with people who can't keep time and/or can't sing in tune.

A few things come to mind.
In my own case, I've been playing a musical instrument since I was 8, and that was over 60 years ago. Although I picked up some basic music theory along the way, I cannot read standard notation, nor have I ever found a need to, nor do I ever plan to. If you do, and can, "good on ya", but not for me.

Two of my guitar-playing acquaintances are at opposite ends of this spectrum. One knows theory, reads music, has played in all kinds of bands and sounds great. The other sounds equally as good but he couldn't tell you what chord he was playing nor what key he was in. Both are "musicians". One has a need for notation and theory, the other does not.

In my last few years of "snowbirding" wintering, I've played in several Jam Sessions with many different "musicians". The majority of them woud have quit long ago if they had been made to learn notation and theory. They do it for their own enjoyment.

If Notes meant "every gigging musician, who wants to be able to sit in with other 'reading musicians' and feel comfortable", then of course they will be better off with notation and theory. But "every musician"??? I would disagree.

LLOYD S