Okay, so I know rats have significance in some cultures - for example, to some Maori tribes, kiore, the Polynesian rat found in limited locations in NZ (due to being outcompeted by Norwegian and black rats) are considered taonga "treasure" - but honestly, what would the ecological harm be if rats went extinct?

Do they fill a vital ecological niche? In New Zealand, they certainly don't, they have supplanted a niche already occupied by our weta - an insect that evolved to fill the niche normally occupied by rodents. (And to show how far it goes, our native owls were the main predators of weta before mammals were introduced, much as how owls worldwide are predators of mice and rats)