Why are most people scared of mice/rats?

They carry fleas and other parasites, posing as a threat to humans and their pets. Mice and rats are more afraid of humans than humans are of them so they try to stay hidden and in their own habitat. Sometimes, they enter our home because they smell food or because there is a point of entry they can access.

I own rats as pets. I think they're some of the most amazing little creatures out there. But most people would disagree with me. When people hear that I have rats they almost always respond with a "Eww! Rats??? WHY on earth would you want RATS??? Of all the things you could own, why rats? Don't their tails freak you out?" Granted, before I owned rats I too was weirded out by their tails, but their sweet personalities quickly won me over and it only took interacting with a rat for 5 minutes for me to get over any weird feelings I had about their tails. 

Before the pandemic when I would have friends over and they would meet my rats, they would always think they're adorable, even pretty. That is, until they learn that they are rats. Then they're all like "Wait, THOSE ARE RATS??? BUT THEY'RE CUTE..." Or they're suddenly  weirded out that I would keep rats and not a "cuter" rodent like a rabbit or hamster. Or they'll think they're cute, minus the tail and feet. Some say their feet look freaky or don't like how the tail and feet are "naked" and thus "feel weird." I think their little hands are cute, but many people find it creepy that they don't have paws like a dog or cat. Some of my friends straight up refuse to call my pets "rats" and instead opt to call them "mice" or "hamsters" because to them those are "cuter."So generally it's a mix of things; the tail, feet, their teeth, etc. But also there's always some sort of stigma people have when they hear the word "rat." Usually they think of a sewer rat or the type that raid their kitchens as pests. Sadly they can't differentiate between sewer rat and domestic rat. There's a huge difference, but to most people they think of the household pests that damage property with all their chewing, and that carry diseases. 

Typically rats have more of a stigma than mice do, and thus are more feared and hated by a large number of people. That isn't to say people aren't afraid of them though. Same with rats, many people can't stand their tails, and are afraid of catching any diseases from them. Really though, it mostly comes down to being afraid of what's unfamiliar. Many people weren't raised around mice and rats, or taught to view them in a positive light. 

But then too, some people just have phobias to different things, even if we know that it's an irrational fear. For instance, I'm afraid of moths and butterflies, even though I know they couldn't possibly hurt me. I just can't stand the idea of them being anywhere near me, and especially not in my house. Could be similar for people who are afraid of mice and rats.

why are you not they stink

I think because wild rats and mice have been known to carry diseases. 

People that fear rats and mice are in a minority.

Then the group that just takes them for granted.

Then the group that know rats and mice and like or love them.

 Social norms

 and they have never actually had the opportunity to see domestic rats.

I have asked people, and a recurring answer is the naked tail.  It's not fear in the ordinary sense.  It's some kind of uncanny thing.  They look cute but the naked tail looks like, but not exactly like, a penis...  It is creepy to them.

Then they hear that they can carry disease, which is actually rare, but it reinforces the creepy factor.  

A rat isn't much different from a squirrel, and they can carry exactly the same diseases, and do the same damage, but most people are not scared of squirrels because they have furry tails.  Not creepy.  

Needless to say, I don't react this way; I am not scared even of wild rats, let alone mice.  I love rodents.  

The secret of nimh movie 1982 cartoon definitely creepy. Shut again start to cry I didn't even think of that but now again that topic