DISSENTING OPINION:
There are no rules on bass nor should there be, period. Any preconceptions of how a bass should be played only limit development and artistic expression. If Jack Bruce and JAE and Macca and Chris Squire and Larry Graham hadn't broken boundaries in their time, the bass world would be a poorer place.
I like bass solos. But I like them to be in a band context, not the whole band stopping and the bassist throwing in some technical chops and the band then returning, that bores me, "bass clinic solos" as opposed to "musical solos". But a bass solo over a harmonic backing (that is the way I prefer drum solos too) where the bass is free to do what it wants is to this day relatively rare in most types of music. Unfortunately, because it sounds nice - whether played with high, medium or low notes. I don't know what that has to do with guitar playing unless melodic solos on all other instruments are somehow handicapped guitar solos too.
And I never understood why an instrument that is fretted up to the 20th fret or more should sacrifice a third or more of its potential playing area for a non-play zone that someone decrees. That just doesn't make sense. A note fretted on the G string at the 22nd fret can have as much meaning as an open E string tone. Even (or especially!) if its unexpected.
Free your mind and your (b)ass will follow. And get an untuned one string boom box if "holding down the rhythm" is all you want to do, why bother changing a note, if you're low enough no one will care? The beauty of bass is the combination of rhythm, harmony and melody - in a word: music!