I don't think that etiquette says we can never make people feel uncomfortable. That's impossible. Etiquette might tell me I shouldn't show up at a party with my new uninvited boyfriend, but it doesn't say that I am obligated to keep him a secret because the knowledge that I'm dating someone new will make a bunch of busy bodies uncomfortable.
A post on FB is also not the same as putting new information in your face and saying "here...you must choose right now, in front of me, whether to accept this situation or not." What it does do, however, is give you the ability, with the luxury of not having to make an immediate, on the spot decision, how you will either move on with our friendship or handle the relationship in person.
You can be as judgy as you want about other people. You are definitely entitled to your opinions. But if you really expect that your opinions do or should shape the decisions of those around you (with very few exceptions), you're wrong. Your opinions shape your behavior...not others'. And sharing those opinions publically, in most cases, is gossip...which is rude.
**You's are general**