I've only ended relationships for lack of physical chemistry/compatibility, or feeling like the other person was more interested in me as an idea of something then a person, or simply growing up and apart. I have to say I've never dated someone with very different political beliefs or ideas about social issues however. I count myself very lucky that I never was with someone who wasn't a good person.
Non-deal breakers for me that were negotiated at various times included little things like whether it was okay to snag fries or share food, leaving dishes in the sink, who does what chores when. But also deeper cultural things such as unspoken expectations around holidays and visits with parents that the other person might not know, how to best communicate through stress, anger, fear and hurt, what kinds of assistance can be expected with certain kinds of work or life struggles, and what kinds of things we would need to take responsibility for and solve on our own. Also when the other person needed alone time, and how best to read each other non-verbally.
Things that aren't questioned -- what the other person wears, what they do with their free time and with who, what kind of work they pursue, what their hobbies or interests are, how they spend their money (the part not pooled for household reasons), what they eat, how they vote --- basically anything relating to their autonomy as an adult individual given mutual honesty and trust.
I think the only style or etiquette things I could right now imagine maybe not dating someone for would be smoking (or you know, drug addiction), or things related to communication -- not letting me know where they were or when they would be home if we lived together so I worried, that kind of thing.
ETA: wait, I just remembered I did date a smoker. Lol, I guess I would say the political leanings/underlying belief system is very important? Other stuff, not so much.