BTW, yes I'm not a big fan of those who are in Democracy trapzing through my culture when they haven't been attacked in that turn. At the same time, the AI does this (read the first posting) & can do it for multiple turns too (ignore your diplomacy requests).
Yes, I agree that human options in SP are more indicative. However, if we want to use that example, you can always defend yourself against the AI if they attack you while you are in democracy. You always get at least the turn they attack as a counter as they don't do the war/peace in the same turn. In fact, you can attack them until they request diplomacy.
So I think that gameplay behavior along with the clear statement from Civilopedia makes it obvious that Democracies can defend themselves when attacked & the diplomacyy spamming to avoid being countered is simply wrong. I'm fairly certain the Firaxis development team would agree with this sentiment even with the patch. So there is no justification for it if that's what people are looking for in this thread. It's very simple:
Attack a democracy & allow for a counter in the same turn. If no counter comes, declare peace at the end of the turn or the beginning of the next turn. Very simple & just how SP plays too. Basic gameplay in a nutshell.
Just look at how SP plays as the topic in Civilopedia is captioned "Gameplay".
People here (yourself included) have argued that you can't refuse an AI diplomacy request. Fine.
However, the AI also doesn't declare war & peace in the same turn. So follow the entire behavior consistently, not just the part that suits your position. If everyone does that, I'm sure there won't be any major issues as it's just common sense: If you declare war this turn, you'll need to wait to the next turn to declare peace (or the very end of this turn if it's obvious no counter is coming).
I don't think we need to split hairs. Just do what makes sense based on the gameplay & the reasonable model is obvious. This is why I always allow for a counter when I'm attacking a Democracy because that's exactly what occurs in SP as the AI declares war on 1 turn & peace on the next (or whatever later turn it decides). So do the same in MP & everybody is happy.