Most tailors advise against it because they can't do it properly. That is a reflection on them, not the alteration. It's not a problem if the tailor really knows his stuff.
I'm in complete agreement that a competent tailor wouldn't hesitate to take on such an alteration; however, many tailors lack the self-confidence and/or skill to attempt it. Â I've been discouraged on more than one occasion. Â Of course, I didn't persist at those establishments: if the tailor felt uncertain about his ability, then, I wasn't going to allow meatball surgery on my Neopolitan jacket, which remains about 3/4" too long in the sleeves. The alteration of sleeve length from the shoulder is obviously a far more labor-intensive and expensive project. Â Can anyone say what the average charge would be for such an alteration? Â For those who have had sleeve length shortened from the shoulder, have the results been satisfactory?