harry potter - Why Couldn't a Time Turner Have been Used to Stop Voldemort?

With the use of a time turner, that opens a whole "Pandora's Box" of possibilities. While the use of one can be problematical, when the Ministry of Magic found out how dangerous Voldemort was, why didn't they simply use a time turner to go back and stop him before he became dangerous?

(I know this does open a lot of plot holes, but witches and wizards don't seem to worry about laws of science, so it would seem strange that magic that seems to easily supersede laws of physics (like brooms that fly without propulsion) would worry about the problematical issues of time travel.)

Answer

This is specifically discussed in the Pottermore moment "The Time Turner". In short, time-turners cannot be used to affect major changes without incurring dire (but unspecified) consequences.

Using them to remove someone as important as Voldemort would, presumably result in massive ramifications:

Even the use of the very limited amount of Time-Turners at the Ministry’s disposal is hedged around with hundreds of laws. While not as potentially dangerous as skipping five centuries, the re-use of a single hour can still have dramatic consequences and the Ministry of Magic seeks the strictest guarantees if it permits the use of these rare and powerful objects. It would surprise most of the magical community to know that Time-Turners are generally only used to solve the most trivial problems of time-management and never for greater or more important purposes, because, as Saul Croaker tells us,

- “ just as the human mind cannot comprehend time, so it cannot comprehend the damage that will ensue if we presume to tamper with its laws. “

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Obviously this is drastically subverted by the entire plot of Harry Potter and the Cursed Child where a new sort of time-turner (one capable of going back multiple years) is used to resurrect a major character.

The short answer would seem to be that you absolutely can use a multi-year time-turner this way, but that the Ministry would rather you didn't, in case there were any dire side-effects.