That's the whole point. Their name is /not/ "Mrs. [husband's first and last name]"

There are definitely people I know that would be okay with being addressed this way. There are many I also know who have expressed that this makes them feel less like an individual human and more like an accessory to their husband.

It's not about how. I don't think anyone would mind an honest spelling mistake for example. The issue is what you're saying about them. If you call them by their partner's name it may mean you either don't care about them more than "they belong to Mr X" or that person's life is defined by the existence of their partner. Those kind of views are decades old and some people will actively fight them.