I think forum etiquette is no more than normal good manners. I would not correct someone's grammar if I were speaking to them in person, and I don't correct any member's grammar, spelling or punctuation on forums.
Not easy for a pedantic former English teacher!
I can ignore personal insults (I think they say more about the poster than about me) but I think they are usually considered to be in breach of forum etiquette.
Finland & Sweden have formally applied to join NATO this morning.