But, from where I'm at, the above list is more like minuses or annoyances or questions of taste; I can't see how a reasonable person could consider them to be actual dealbreakers -- things that so much impact your enjoyment of a game (or your politics) that they're what I'd call "legitimate" reasons to boycott it.
Anyone care to enlighten me?
Of course it is a subjective thing.
But take Indigo Prophecy as an example: Those times, where you had to press some keys in a certain order to progress the game were very annoying and immersion breaking for me, but i might have swallowed them.
But when I got to a scene, where you were in an appartment and looked around and after some time the police came in and you lost the game if you didn't do several things (coverup of some evidence against you) fast enough before , I simply stopped playing. My only save game was after having already having lost to much time, so I couldn't get on without restarting the game, which I had no reason to do.
This was in fact one single mechanic which was reason enough not to play the game.
From such experience I expect that a similar mechanic would ruin the game for me. That is why I wrote "a REALLY timed dialogue". If for example I can pause the game at any point, such that the timer is not a real-life timer, I will have no problem with it and will consider it being only an annoyance.
Moreover, I like games with choices and consequences, so I expect that dialogue choices have impact on the game (otherwise you can skip the dialogue anyway) and I don't like to make important decisions under time pressure.
For example I don't play real time RTSes with timed missions and such stuff.
If the decision is only "fight" or "give money" and the further story is not depending on this deciscion, a timer would be merely annoying, I admit. but in that case the game wouldn't be very promising for me either.
So yes, you are right that it is not ideal to base decisions on one single game mechanic before knowing the game. But if I deduce expected outcomes from former experience with other games, I am sceptical, whether this can work out good.
Of course a claim like "if [this and that] I will not buy it" is never as absolute as it sounds. If I learn from reports of other players (e. g.in this forum) that the timer doesn't exist in this form or doesn't have the impacts I fear, then I will of course consider buying the game.
Edit: Another example would be the enemy respawn mechanic in "Dungeon Lords". It was only one mechanic but for me it was reason enough to stop playing the game and consider it one of the worst games ever, in fact. Similar with the level scaling in Oblivion.
Another edit:
In fact a strong story may allow me to forgive such things. If Dungeon Lords or Oblivion had started the story in a way which would make me curious enough to go only only to see how the story progesses, I would have ignored those mechanics. Both games didn't do that.
In a game like "The Witcher" I might have ignored those mechanics. In fact recently I played an RTS, "Paraworld", where I even swallowed two timed missions in order to learn, how the story continued and because I loved the atmosphere and the other game mechanics. But still I prefer to replay "Spellforce" (the first one), which has an interesting story, RPG-elements and no timed missions.
Third edit: Whether it is possible to enlighten you is beyond my control.