Nasty? I used to keep rats as pets. They’re actually quite nice as pets, and they’re actually surprisingly tidy, grooming themselves and also keeping their living spaces as clean as possible. But they are smart, and may be able to escape some enclosures. They’re also big enough to deliver a very painful bite, so I can see why you’d rather work with mice.
But if anyone’s considering a pet, I do recommend rats.
I can echo that rats can be great pets! They are relatively clean, quiet and can be almost affectionate. If handled gently from an early age, they are very amenable to human contact. I had a couple of rats over my junior high & high school years, some were taken home after non invasive science experiments in biology class. The females were the best – but most of the males were nasty!
This reminds me of a cartoon I saw years ago. It showed a line of dead rats, each labeled with what killed it – things like toxins, air, water, etc. The last one was labeled “Sex” and was the only rat with a smile on its face.