The decision to switch from the polytonic to the monotonic system belongs to the Greeks and I have no right to interfere into their choices, but I can give my opinion as an Hellenist, translator, reader of ancient Greek. My testimony is also the one of a man who works on oral restitution of ancient Greek according to scientific methods (using data from historical and comparative phonetics) and who has an artistic practice since I direct the comedians of the Demodocos company.
Like any spelling simplification, it moves those who learn the new rules off of their past.
Similarly to the reform of Chinese which has, in my opinion, made the access to literary texts very difficult, I'm afraid that the simplification of accents of modern Greek will cut the Greeks away from their very rich linguistic and literary history. The Greek alphabet, accented by Aristophanes from Byzance, at the 2nd century A.D., has allowed to the language to transmit the manner of modulating melodic heights of syllables, and is able to do it even today, even if the evolution of the language has crashed the height accent in favor of the intensive one.
The, obsolete for some, presence of accents invented by the Grammarian of Alexandria, was an extremely precious testimony of the way an earlier stage of the language was functioning.
This presence of accents, like the community of some linguistic and lexical practices, gave the modern Greek language the possibility of an affinity with all stages of its history. I fully understand that some people regret that this precious link has been broken today, after having been kept for so long. (Translated by Y.H.)