Unlike your other respondents, my wife and I live in Morelia--and have for 3 years. We retired here from the USA. I am very involved with the largest, oldest expat group here. It is small, but active.
As for violence or danger in Morelia, I can only say that if you didn't read the news, you wouldn't know it existed inside the city. There have been some recent incidents on highways leading in and out of Morelia, but those seem more like muscle-flexing by narco gangs. As one of your respondents said, though, if these kinds of things make you apprehensive, perhaps Mexico is not for you.
Morelia is a great place to live. The respondent who recommended Patzcuaro raises an alternative that many expats have chosen. Patz was not our choice because it is much cooler, and because it lacks the cultural and shopping pluses of Morelia--symphony, theater, movies, lots of restaurants, lots of shopping options, etc. But it does have a more concentrated expat group than Morelia, and housing is less expensive there.
Some people choose to return to their home countries to live after spending time living in Mexico--often as they reach a point in their lives where they want family nearby during the end of the aging process. People who refuse to or can't learn Spanish also have done that. But I know folks who have been here for many years and love it.
You can only do so much on the internet. I suggest you do what many expats have done before considering a move to Mexico. Come and spend several months in Mexico and check out a few options. It is a big commitment to make such a move--where you will live under different laws, speak a different language, exist in a different culture. I'd recommend spending at least a month in any city you might consider moving to. And if you do move, plan to rent for several months before buying. I would certainly suggest you include Morelia as a place to check out.