The concept isn’t bad per se, but the execution is often one dimensional “ooh spooooooky evil dead guy has come back to life because of a curse. They’re going to kill unless we kill them”. That’s what’s bad. There’s no thought to how an Ancient Egyptian might feel suddenly being forced back into their body after 3000 years. People forget that mummies aren’t just plot devices, they’re a cultural practice and involve actual people. They’re not a Hollywood monster, they’re real people from a real civilisation with culture and history. And we cannot separate this from colonialist thinking as they’re deeply entwined. The only reason you have mummy coming to life stories is because of colonialism and racism. The Victorians were the ones who started the morbid trend of “ooooh spooky magic body from a culture we don’t understand comes back to life to curse us all”, by literally desecrating them bodies of the dead at unwrapping parties. Hollywood then played on this notion, further cementing it into people’s lives because “no it’s ok they’re not like us, use magic, are spooooooky and weird”. It makes a mockery of the body of a deceased person, and ignores the very reality of how an Egyptian person would feel slammed back into their body.

The Ba was designed to come back to the tomb in order to receive sustenance from offerings left by relatives of the deceased, which in turn sustained the deceased in the afterlife. The Ba does not return to the body to inhabit it, it’s job is to take the sustenance, reunite with the Ka, and become the transfigured Akh of the deceased. If a Ba is trapped in a body of the deceased and that body is reanimated, it prevents the deceased from receiving sustenance from offerings, and jeopardises the deceased’s existence in the afterlife; for if they do not receive the offerings from the Ba then they will die a second time and fall into Nun. That’s a horrific fate for an Ancient Egyptian. They’re yanked from Aaru, their literal afterlife paradise, into their 3000 year old corpse, and in doing so may very well lose access to Aaru and suffer Second Death. A complete non existence. They’re not going to be ok with that.

If you truly want to write a “mummy comes back to life” story, you have to take that sort of thing into account. You have to give them agency, and not the one dimensional “gonna kill you all” bad guy they’re portrayed as all too often.