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Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] why is Voldemort so fear inducing?

I mean, he is a normal wizard with higher than average magical powers. It wouldn't be unreasonable to say that there could be a handful of other magicians with magical powers close to those of Voldemort.

In the real world it would be similar to having a criminal with amazing shooting skills who is also the strongest human on earth. Yes, he would be threatening to handle one on one, but he'd be no one man army.
gpt
bit of a ramble, but here we go.

Voldemort operated in a world where stealth vastly, ridiculously outmatched detection. In the Wizarding world, if you wanted to hide, and you knew enough magic, nobody and nothing could find you (Fidelius). The government itself had no defense against Polyjuice potion imposters (as we see in the books), and nobody seems to have any defense against the Imperius Curse. In the Wizarding World, terrorism isn't just an effective battle tactic; it is the most effective battle tactic. 

Essentially, Voldemort was so fear inducing, because he had the good luck to be operating in a world set up to be incapable of defending itself from him. The way magic seems to work (and is used) in Harry Potter, the attacking force always has a ridiculous advantage, to the point where three teenagers, with only one adviser, were capable of breaking in and out of the most secure bank in the country with minimal consequences. That's how effective stealth and mind control is in the Harry Potter universe. Shapeshifting is so overpowered, that Grindelwald himself (the most wanted man in the world at the time), managed to work at a pretty high ranking role in the American Auror department. Notice how Voldemort only lost once he had conquered the government, and so had stopped being a stealthy, attacking force, and instead became a standard dictator. The moment Voldy marched his forces against Hogwarts like an army, instead of having them use the hit and run tactics that had been so effective before, is the moment he lost.

Plus, powerful wizards in Harry Potter seem to be exceedingly rare, and have powers their peers can barely dream of. Nothing in the movies or the novels has come close to what we saw when Dumbledore fought Voldemort in the Ministry of Magic. And the very nature of magic in Harry Potter means that being the more powerful, individual wizard is ridiculously important. Think of it like this. Imagine if anybody who could beat you in an arm-wrestling contest, could also then read your thoughts, or turn you into a newt, or instantly kill you in one blow, or take control of your mind and have you do terrible things, or make you tell them all your secrets, etc... and the leader of the latest terrorist cell was also rumored to be the strongest guy around. The sheer amount of power a wizard can exert over another wizard is so vast that individual strength kind of becomes the be all, end all.

Harry Potter seems to take place in a world where personal security should be of the most utmost importance, and yet is given almost no consideration at all. Losing a duel could mean spending the rest of your life as a mind-slave, and yet important public figures don't seem to be afforded security details, and defense is allowed to be the most neglected subject at Hogwarts. They know shapeshifting exists, and yet there seems to be no automated way of detecting it. The Fidelius charm means that anybody wanted by the government could literally just go back to their house, cast it, and be completely untouchable 

The entire society of the Wizarding World seems to hinge on everyone being so contented by the "First World +" life they can lead with magic, that there's no one malcontent enough to become a terrorist or criminal. Maybe that's the reason their only prison is a literal frozen hell in the middle of the ocean, patrolled by soul-sucking monsters. When crime is so easy to get away with, the punishment for getting caught has to be pretty damn harsh if its going to be an effective deterrent.