I think the issue for me is the difference between public and personal space. A phone conversation in a corner where I hear snippets or murmurs is in personal space; a phone call that Is loud enough to be heard several tables away is in public space.
Short, quick calls to check on the kids, or to meet at a pre-ordained spot, are permitted in public space, but extended screaming, abuse, yelling and arguing belong in personal space. The other party can hang up, but the rest of us are stuck with you.
Sensitive, private, or highly personal matters should be discussed in personal, not public, space. Fighting with your partner, firing an employee, discussing your colon issues, or making arrangements to cheat on your spouse are to be discussed only in private space.
Crowded settings where people are packed together and retreat is impossible, are public space. In these public spaces, treating them as your own personal space is inconsiderate--and, yes, rude. If we all decided to do that, life in cities would be unbearable and airline travel unthinkable. If it is truly an emergency, we will bend the rules and do what we can to provide you with more personal space in a public space even if it makes life less comfortable for the rest of us--much like a medical emergency on a crowded plane. It's called goodwill.