The reason in books: muggles will oppress or kill them, falls flat in the face of their overwhelming power. And the fact that they've never had much is an issue.
I don't remember if it was a main book or one of those charity publications but she specifically decided to mention that witch burnings, when they caught a real witch, just resulted in the witch casting a spell that made fire tickle a bit.
I didn't really think they actually covered that plot point well.
The biggest problem iirc is a duplicated loaf of bread has the same expiration date as the original, so you can't actually make bread last forever with duplication without it getting moldy. Preservation charms wear off the same as muggle preservatives do.
But I don't see why dried or smoked food couldn't be duplicated for months or years. The biggest threat would be scurvy at that point.
Even with those limitations, duplication would still allow food producers to make less food go a longer way. Smaller farms could feed more people, reducing pollution. You could duplicate the food at the point of sale, which would drastically reduce transportation costs as well as traffic. Hell, cities could have small farms and fed themselves. It would also drastically reduce water consumption that is used in farming, reducing droughts. Producing and transporting food is a massive contributor to global warming. Farms and ranches take up tons of space, all that land could be returned to its natural state (I bet wizards could speed that up).
If wizards showed up with the cure to cancer and fed the hungry they'd easily have 1/5 of the world's population on their side. Unfortunately the wizarding society is extremely exploitative of animals, even worse than the average muggle.
I get that wizards were persecuted and don't want to have muggles expect them to solve all their problems, but they could literally save the planet.
Absolutely! Wizards can also cast longer-term enchantments in addition to duplicating food, so they could also provide self-stirring cooking pots and self-fueled stoves and self-cooling ice chests. That doesn't even get in to Arthur Weasley tinkering like the flying Ford.
Does it, tho? Wizards are powerful, sure, but they're severely outnumbered, and almost completely ignorant of technology. What's your Avada Kedavra, that moves slow enough that untrained school children can dodge it, gonna do against the Mother of all Bombs? Or a nuke?
The issue is that wizards can instantly wage a guerilla war. All it takes is Muggle Studies being taken seriously and integration in muggle society. Then it's impossible to identify them. Wandless magic could be a focus to be certain you're never carrying an identifying marker.
Then the wizards don't need to attack. They can destabilize the economy by duplicating money, precious resources, etc. These will deteriorate eventually but cause chaos and devalue the economy for a time. Imagine taking a $100 bill and just duplicating it to prop up your car-wash business as a front. But that's baby-level chicanery.
The real sauce is the mind-control. Imperio (who cares if it's unforgivable when you're at war?) and more importantly the Memory Charm and False Memory spells. Let's just get in there, stun a very important person (start low, work up) and insert the memories you need to get them to act accordingly. Remove the memories of that transaction and boom! Access to the most powerful people in the world and the ability to influence them. Now a wizard has their finger (remotely) on the nuclear button!
Seriously. Voldemort was an idiot. He used basic terror tactics for years and the only reason he wasn't killed quickly was because Magical Britian was written to be as stupid as possible because Rowling was writing a children's story about incompetent leaders.