Because it potentially has a massive cost with only very uncertain and mild positive effect. If the civ you denounce turns to hostile, which usually is quite permanent state, you lose thousands of gold and science beakers from trading and RAs. The only thing you get back is a mild positive modifier to denounced civs enemies, which in practice is probably almost meaningless. Negative modifiers tend to last longer than positive ones, and you can get civs friendly or to even declare friendship without denouncing their enemies.
Or alternatively, you'll get into an RA and they DoW on you and you lose your gil and beakers. You seem to have a pretty black and white view of every issue we've discussed. But diplomacy delves into shades of grey.
If you're idea of denouncing is randomly popping up and denouncing real friends because you plan on attacking them soon and want cover for your warmongering, then that's a problem with your playstyle.
Denouncements act as signals to the world community on 1) how trustworthy one of you are 2) who you dislike and alternatively who you could possibly work with against a common enemy 3) how trust worthy you are.
If you get backstabbed and don't denounce, which I believe is the issue that started the discussion on denouncements, then no one would know and you wouldn't get brownie points.
Declaring war probably has a even bigger negative modifier to the target than denouncing.
Again, it's not black and white either/or. Depends on the situation. In the context of your comment, you're talking about joining in co-op wars, and I'm saying you don't get digned by your friends if you don't join.
Now, in situations where one friend is asking you to declare on another, especially with DoF active, I naturally decline. But I get plenty of co-op war requests on real pariah states.
Killing CSs seem to have some kind of global negative modifier. That is conquering a CS annoys every neutral Civ. If this is true, it's a very bad thing to do.
For the third time, killing a CS = killing off a Civ (ie: wiping out a civ from the game, every last city) So yes, it has a negative modifier.
You can get away with killing 1 CS just as you can get away with killing 1 civ in most games and play like as if nothing happened, even if there is a penalty against you in the background. Naturally you need to be able to defend yourself regardless of what you do, or you'd get picked on sooner or later even if you don't kill anyone.
Well, I've done it for a mistake.
Destroys your diplo for the rest of the game.
That's a backstab and the AI will denounce you for backstabbing them ,which turns the world against you as untrustworhy. This Goes back to my earlier point about denouncements as useful signals in the game.
Only the victim of the backstab gets the 'you've been backstabbed' diplomacy message so if you don't denounce, the one doing the backstabbing essentially got away with it.
And yes, in some situations you
CHOOSE not to do it for other reasons, like maybe you want to get more gold from them. That's what diplomacy is, a set of choices. Not black and white absolutes that you keep going back on. Never denouncing and giving trade as a flimsy excuse is not an optimal strategy. Most of the time, the AI doing the backstabbing aren't a good trading partners anyways.
"Dynamic cliques" are more or less the same as no cliques. Negative modifies can be quite permanent (so there are long lasting "cliques" where everyone hates the human player), but positives are not. That's the reason why you shouldn't try to join any dynamic clique: it's likely you will make permanent enemies, but it's unlikely you will make long lasting friend.
A clique is a clique. I used the word dynamic to describe the changing interests and groups as the game progresses. Grouping come and go in this game. The clique itself is what it is, civs with a close relationship you can count on as friends. Continuing to insist it doesn't exist does underline perhaps why you're having so many problems with the AI?
Another thing to notice is that there probably is an anti-Human bias in diplomacy. It seems that for AI civs negative modifiers vanish much quicker. At half game, just about every AI probably has denounced and/or declared war to every other AI, captured a city state etc. Still they are making research agreements with each other. If human tries to join to "dynamic diplo" of the AIs, he soon ends on situation, where he can't make any RAs and barely gets half the money from trades.
Play with infoaddict. There's a global relations web showing what the AI think of other AI civs. The assertion of an anti-human diplomacy bias doesn't hold water in this regard. But then again, every Civ game has had people say there is a bias against human players, until of course the bias is clearly for human players, at which point the human player says the game is 'fair'. Goes to show our own biases in subjective readings of the AI and RNG results.
Trading is easy on CIV5 as there seem to be only very mild "you traded with our enemy" -penalty. On CIV4 that penalty was substantial and forced you to think who you wanted to trade with. Generally diplo on CIV5 is much easier to handle than it was on CIV4. Now actions either have drastic negative consequences without much positive (denouncing, declaring wars, capturing CSs) or have virtually no effects on diplo (trading, choosing SPs). If you struggle with diplo on CIV5, you are probably doing something wrong.
Trading penalties is there, but what drives diplomacy are the dof and denouncements.