Full names, at least in the USA, are sometimes used by parents to address their children when they are in trouble. Rude might not be the right word but potentially at least jarring. I have never experienced it or seen someone react that way from text but I have with verbal addresses.
edit some conversations about the topic for reference since it is harder to google for than I initially thought it would be.
https://www.quora.com/Why-do-parents-address-their-unruly-ch...
https://www.reddit.com/r/AskParents/comments/pj6aqw/why_do_y...
Are you or your people Asian?
Though, even in Asia which names to call a person can differ wildly. I'm not sure how your personal ideas about rudeness are relevant here.
Yes.
> I'm not sure how your personal ideas about rudeness are relevant here.
Names matter.
So what you’re actually saying now is that any inferred form of address may come across as rude, which means you original suggestion is plain incorrect: splitting given name and family name does not allow generating a genetically never rude form of address, because you can’t know whether the user’s culture favours given names, family names, full names, or even none of the above.
And that’s before getting into honorifics and titles.
No, that is not it.
Yes, it very much is. You’re declaring that one form of address is rude to your culture, while acknowledging that it is proper to an other culture.
This means the two cultures are completely incompatible on that point, and thus no generic munging method can satisfy both.
And yet your original suggestion was to do exactly that, just in a form suited or at least compatible with your cultural sensibilities.
For westerners you might want sunny, good-news messages to say "Hi John" but for an apology for a problem (like a delay or cancellation) you might want to use the more respectful "Dear Mr Doe"
On the other hand, this discussion has plenty of examples of why separate 'first name' and 'last name' fields don't work in all cultures. And I think we can all agree that asking people for a name and two desired forms of address ready to e-mail them in two different tones would be a very unusual sign up process.
I'm not sure there's any universal, fully respectful way of doing this across cultures.
Just add a field for the desired form of address, or a nickname.
> Addressing a person by their full name can come across as rude
Stuffy, Maybe, but rude? Calling people by their first name is rude. Calling people by forms of address which don’t exist is rude.