So, although the question-asker is being downvoted, your response does actually cover interesting discussion topics, and to summarise, the answer could be that the systems and conventions need to change?
- I believe in the UK (where I live) one has all of the legal and financial implications automatically when a relationship reaches a certain age (3 years I believe). Legally you would be treated the same way as if you were married.
- Friends and family; My family certainly feel this way, my wife's I'm not sure. I'm "mixed"-culture/race/etc so some of my family have different cultural views. My wife and I don't feel strongly either way about how our children deal with this when they grow up, so perhaps our (millenial) generation is changing the "social" side of it already?
- Legally I believe you have all of the rights you describe, however, it may be more difficult to prove the relationship without a piece of paper. We've had to present our marriage certificate for various things relating to our child(ren) for example.
- It _should_ have no effect on your ability to purchase a home in the UK
- There is a tax benefit for low income couples in the UK, but I believe our law doesn't specify "married".
- I don't know how any of this affects UK citizens abroad as I've never looked into it.