Yes funny, this is one of these religious topics. Of course any purist would hate the idea to have people think he might be so much of a beginner that he would need these little helper lines, thus he rather wants to stand up as a mature player who can do fine without them. It is a very legitimate psycholical phenomenon. I don't feel my maturity questioned though just because I like the lines. You could surely drive a car without a speed indicator if you got used to the feel of speed. I enjoy playing unlined fretless basses just the same. And they look as pure as a fretless instrument can look. But it is just looks. What do I care about looks on an instrument when it comes to usefulness? Ok, I do care, otherwise I wouldn't be on this forum, but besides that, I did play unlined fretless and lined fretless.
Now, who says you do have to look at your fretlines just because they are there? What a silly idea is that to believe you wouldn't be able to take your eyes off the instrument just because it has these little lines on them?
And who says you have to play your pitch at the spot where the line sits? I play it in front and behind the lines wherever the pitch sounds best, it is still a fretless instrument. I play it exactly where I would play it on an unlined fretless. Fretlines are just guides, like side markers. Do you leave away your sidemarkers just because you won't find them on an upright bass or a violine? Maybe you would and I am sure you would be able to play just as fine. I just have additional options available with fretlines or side markers. Whether I make use of these options during playing or not is purely up to me and usually a matter of the musical situation itself. Sometimes I do, sometimes I don't.
I for my part have never understood why purists get so upset about other people's lined fretless instruments. There are discussions about 4 string vs. 5-string, flat strings vs. roundwounds, bolt ons vs. neck through, etc. The fretlines discussion is just as much dependent on personal taste as any of the other. I don't think Mr. Pastorius was ever embarrassed at his fretlines and he surely could have played unlined fretless instrument if ever he wanted.
I guess, you decide what is right for you and that is all that counts. Other people will chose differently for themselves and that is just as alright.
Hartmut