Lets take a look at how we see classical guitarists and standard musical notation. My perception of a classical guitar player is someone who is tied to the sheet music from day one. He will not play a note unless it is written on the page. Furthermore, he probably belongs to the school of thought that says that tablature is an inferior form of written music. Incomplete and useless for learning new pieces.
My perception of the classical guitar player cant be entirely accurate because there are lots of classical guitar tabs available on the internet, so maybe attitudes are changing gradually.
Tab is not a bad thing in itself. It is a perfectly good way to quickly find the notes on the guitar as you learn a new piece. The fact that tab does not include all the information you need to play a piece has given birth to a widespread prejudice against tab simply because many musicians think that the written notation should be the sole source of information needed to learn the piece.
Where guitar tab falls down is if you use tab to learn which notes to play, you also need to have an audio record of the piece to refer to in order to play the notes in time. So yes, tab is an incomplete source of music notation but if people want to use tab anyway, then that is their concern.
Back in the nineteen seventies classical violinist Yehudi Menuhin collaborated with sitar player Ravi Shankar on some records. The resulting music was fantastic but Menuhin had to have his music written for him whereas Shankar was able to improvise his parts. So, music notation gives us a more complete representation of the music but if we rely on it too much we learn music in an environment that does not foster musical creativity. The classical guitarist, at least in my mind, is concerned with expressing the composers music through his relationship with the guitar. Improvisation and creativity of any kind are not necessary.
If you want to learn classical guitar and to read standard musical notation then there are a number of books you can work through to get a grip on sheet music written for guitar. If you work at it for a month or so you will have an understanding of single note melodies written to be played in the first position. There is a number of pieces by Sor, Carulli and Carcassi for example, which you can get a great deal of satisfaction from playing using your new grasp of sheet music.
There are some great books available for learning classical guitar through music notation, the tutors by Aaron Shearer, Fred Noad and Christopher Parkening are obvious examples. These books will give you the full story to learn a piece of music but learning tab as well gives you access to a broader appreciation of music and the opportunity to discover parts of your musical self opened up by the work of learning music through tab.
Of course, it gets more difficult as you begin to learn pieces that contain chords in the melody and more than one melody line. The task of learning which finger to use to play the notes as well as the left hand fingering begins to make learning new pieces more tedious.