tl;dr, with a good degree of repetition, I'll bet.
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Firstly, we're not really talking about aggression vs. passivity anymore, are we? I'm on the side of aggression, myself, in that you have to.. well.. actively scumhunt. Whether you do that by grabbing an argument and slamming it into someone's face repeatedly, or by doing tricky mind games to see what falls out, or by being a vigilante and mainly just trying to keep a low profile so you can keep trying to kill scum at night... it doesn't really matter, the merits of any given strategy change with the games (there is a metagame, people do follow it, let's not pretend there isn't!) I don't, in fact, see much point debating the details, as they'll really just add to the ever-growing DLMafiaMetagame.
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There IS no 'serious business mafia' environment, and we can't really draw comparisions with it. You can't form teams, there are no prizes, etcetera. People are only playing, presumably, for the enjoyment of the game. All of us are 'playing for fun', even Otter and Alex, as difficult as it may seem to believe. Fun is our primary motivator.
Yet in this, as in any game, there is a competetive element; the desire to win, and if not win, to at least improve. This applies to casual groups of gamers as well; isn't the whole point of playing fighting games, for instance, to test your skill against other people? Isn't the enjoyment derived from the competition involved? I can't hold a desire to improve and get better as bad; the main fun is in competeing, and if play just stays at the same level and nobody really tries to improve... it just stagnates.
As for playing against people better than yourselves, two things. Firstly, Alex's link. Sirlin. It's great stuff, it says more about competetiveness than I easily can.
Secondly, mafia is actually pretty cool about this! Much better than your usual fighting game in a casual scene, because it's self-regulating! Let's say you have 10 friends of varying degrees of skill at, say, Tekken; the best ones will prefer to take on the best ones, and so on. Yet in mafia, the best player is likely to get NK'd night one, or when he does inevitably make a mistake, people will pounce on it, out of paranoid (he might be scum!) or maliciousness (he's town, but I'm scum and hate him!). Either way, whislt having varying skill levels compete against each other might well be unfun (particularly if the gap is very wide), in mafia I don't think this really applies due to the nature of the game itself.
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Arguments. That's what this debate seems to be over.
Iff you're going to get upset at the way someone criticizes your play in-game and take it personally, you're missing the point; they're hitting your argument, most likely. If you can't actually defeat their argument, then it is, in all likelyhood, a sign that it wasn't good enough. The thing I think people don't entirely get is that there are two parts to an argument in this game.
-The conclusion drawn from the argument, and whether it's correct or not.
-How convincing it is.
If you're a townie, you're hoping your argument is correct, and you also want it to be as convincing as possible. If you believe you're right, forwarding that argument relentlessly, defeating counterpoints, etc- this is the thing to do.It's also to your benefit to undermine the opposition.
And that's what I think people have the most trouble dealing with- because the actual moves in the game, in the form of lynches, are the key to victory. Those aggressive players want to win and thus they will, in fact, see a need to ruin the arguments of others. Perhaps even if they think those other people are town (for whatever reason), because you need to try and ensure victory, and a wrong move is a wrong move regardless of what side it comes from.
Civil debate is all well and good- but if being more aggressive can ensure that the odds of your argument being accepted go up, then it becomes a war of escalation, where the first townie to think he's right can up the ante and come out swinging. And since scum can guess at this too, then they can tune their play to the current level of debate- either to push forward a lynch or to make a particular opponent look foolish, when his aggressive argument comes out wrong.
If all you do is just take an aggressive argument badly, get upset over it, whatever- that's not actually refuting the enemy argument, which you should be able to do if you think you're right. If the game comes down to an impasse (as it almost certainly will), well, votes will ultimately decide everything.