An Urtext edition is one that adheres as much as possible to the original composer's manuscript (or when that is lost, early editions). Of course, it is a good thing to know the score not yet interpreted by editors, and it seems better that the players are allowed to decide themselves.
But here are my doubts:
The editors may help the reader to better decide the dynamic and articulation. These markings may have been regarded to be trivial and well known by the composer's time, so were left out by the composer, but may be mistaken by modern readers. For example, Urtext editions of J.S. Bach's keyboard work usually show no slur, but does that mean Bach always intended non-legato? No.
The composer's manuscript may contain errors. In parallel passages, the composer may have drawn a slur in the first occurrence, but forgot to do so in the second passage, and the Urtext edition reproduces such discrepancies, making the reader to wonder there is some significance. I recall this is the case of Beethoven's (so-called) "Appassionata" sonata's first movement.
In a Baroque piece, notation is sloppy. For example, a two-voice passage may be notated as single voice. And a short note may be notated as longer note, so as to save space of rests (see Charles Rosen, Beethoven's Piano Sonatas). In such cases, I believe, it is appropriate that editors modify into modern notation according to their judgment.
Considering these, I find the concept of "reproducing the original intention" problematic. What are advantages and disadvantages of using Urtext editions?