I would never play a fretless without lines, it's ridiculous to expect someone to never look at their neck when they play (I have seen the best bassists in the world do it), and I always have to laugh when someone thinks any of this stuff relates to professionalism.
Find me one double bassist, cellist, violist, or violinist in any orchestra that is looking at their fingerboard while playing. Find me one pit orchestra bassist or guitarist that is looking at the fingerboard of their instrument while performing a show. Do trombonists look at how far they've moved the slide to determine what note they are playing?
Currently I'm making a bit of a push to get very familiar with my Conklin GT7 as a two-handed tapping instrument. I'm using the RealBook (standard G clef version), working my way through the chords page after page. And trying to gradually work in chords, chord melodies, and straight melodies with my right hand while improvising basslines on those chords with the left. It would not be possible to do that while looking at the fingerboard.
Obviously, if you are performing the same dozen songs at every gig you need not look at a page of music. But bear this in mind the next time you complain that your band can't get bookings and that those bar gigs ain't paying much: If you could read, your chances of getting good-paying work would immediately soar. Becoming dependent upon gazing at the fingerboard eliminates that possibility.