The important thing with a game like diplomacy is that you play it with other like minded players - it is very much a game for people that can compartmentalize their gaming experiences and enjoy being absolutely ruthless. There is a big difference in being competitive and playing to win and being a ruthless backstabber and enjoying playing with other people that can be equally ruthless. Any game can be played either way, but normal board games are meant to be competative, but not nescessarily ruthless, where diplomacy is meant to be played that way and if you are not playing it that way with other players who feel the same, you are not getting the intended experience it has to offer - a good game of diplomacy is more like a live action war based role playing game.
The other games you mentioend I have not played, so I can not comment on them, but I have heard the names and none of the other ones you mentioend are ones I associate with the level of ruthlessness that is expected in Diplomacy (it is in a league of its own). After watching the brief review of intrigue, it looks like the kind of game that being ruthless and scheming is the intended way to play, and the consequences to other players may be more detrimental than in some games, but its more in the realm of games like 1830 or the Game of Thrones Card Game (both of which often get called "evil games" by my friends that don't enjoy ocasionaly stepping into the role of ruthless schemer). Although such games may not match the pure evil of Diplomacy done right, they can indeed result in hurt feelings when playied with players that don't appreciate that style of game play.
Twilight Imperium is one I have not played in many years, but aside from length and depth of gameplay, it did not strike me as being in the "evil" catagory of games, but there are many gamers that simply don't enjoy games with a strong conflict element (I forget how much conflict in in Twilight Imperium, but I rememebr it being a "multiple paths to victory" type game), so once again, knowing the preferences of your friends you plan to play with is important.