Updated: Oct 10, 2020
The Time Turner should not have been introduced in Harry Potter.
Yes, I’m glad it saved the lives of Buckbeak and Sirius Black but the mere implications of its existence are harrowing.
The only Time Turners in existence are supposedly either under Ministry control or closely monitored by the Ministry of Magic. Since the story is told through Harry’s eyes, we have no idea what the Ministry of Magic does with time travel magic outside of the context of this story. To set the stage, the government in the Wizarding world basically has time travel at their fingertips to modify any small decisions.
Dumbledore scoffs at Fudge and Snape’s suggestion that Harry and Hermione can be in two places at once. But if the Ministry gave approval to Hermione Granger, how is there is no chance that Cornelius Fudge isn’t aware that the one Time Turner at Hogwarts is in the property of the one person whom Dumbledore said couldn’t be in two places at once?
The Time Turner saved two lives in the Prisoner of Azkaban - but if there was a possibility of saving a life using a Time Turner, why weren’t more lives saved? Isn’t it a moral obligation to save a life if you have the capability to do it at your disposal?
Dumbledore basically gave two underage teenagers permission to travel back in time and release a harbored fugitive knowing full well that they could be killed and or compromised if they’re caught. What in the fuck!?
Hermione mentions that Wizards have killed their past or future selves but how does this work? Do entire timelines and family lineages change because of one person using a Time Turner? Imagine if you just exist one day but then your father uses a Time Turner and kills his past self. Do you still exist?
JK Rowling does address the drawbacks of the Time Turner on Pottermore:
I solved the problem to my own satisfaction in stages. Firstly, I had Dumbledore and Hermione emphasise how dangerous it would be to be seen in the past, to remind the reader that there might be unforeseen and dangerous consequences as well as solutions in time travel. Secondly, I had Hermione give back the only Time-Turner ever to enter Hogwarts. Thirdly, I smashed all remaining Time-Turners during the battle in the Department of Mysteries, removing the possibility of reliving even short periods in the future.