* They over-generalize from personal experience. They will for instance make blanket statements regarding relationships based on only ones they have had. Some will even accord their personal encounters the status of experiments (which naturally confirm assumptions they have made regarding human nature).
* They tend to elevate their own personal tastes to the status of moral truths or natural facts. Such silliness as thinking European orchestral music is intrinsically better than other kinds of music is an instance of this (which may seem a trivial case but I think it demonstrates a kind of snobbery and chauvinism).
* They only countenance one explanation for a phenomenon rather than the possibility that things have more than one cause. However they also use different basic assumptions from issue-to-issue. Sometimes they will be biological determinists (saying our behaviour is limited by gender for instance). At other times they will be meritocratic (saying we can do anything as long we make an effort). If these issues enter into the same conversation it can be difficult to understand what they are saying or why.
* They use simplistic models in which everyone gets put into boxes. The fewer boxes they use the better they like it. A handful of anthropological 'races'. A few hazily-defined classes. Only two brands of politics. They also tend to define the boxes in such a way that conflict becomes necessary. Hence we get things like 'the clash of civilizations' even if huge differences exist both within and across those supposed groupings. How can you possibly understand the motives and actions of others with such simplistic models? I suspect many of them have a misanthropic lack of personal development.
* They act as if what you are is more important than what you say. They will take an interest in things like your surname or mugshot to help them define your demographics. This can help them anticipate and characterize your motives rather than focus on the debate itself. According to them I'm a chardonay-sipping hipster with 'white guilt'. What is a mikshake-sucking pink-complexioned suburban nerd with a well-managed case of German Guilt to do?
* They prefer conversations to be scripted rather than improvised. This is partly why they want you to fit an anticipated role. You will then say what they expect and they can respond with a prepared selection of statements, phrases and terms. If you defy the expected script then you undermine what they had planned. Especially If you partly agree with what they say (you for instance offer different solutions to an accepted problem) you undermine them. A more reasonably-minded person may try and explore the common ground you have just opened. But the hostile arguer will become suspicious of your understanding or concern. They may even dive back into their kit of jargon and find some label to help dismiss you as an agent provocateur sent to confuse them.
* They see intent behind problems rather than the possibility that things happen by accident. How many times do we discover that an issue arose from lack-of-competence rather than corruption? How many times was a seemingly offensive act something entirely different? This mundane reality undermines the black-and-white narrative of too many online antagonists.
* They distort the power levels of both themselves and others. Sometimes they are powerful and will declare how the future belongs to them. At other times they will lament how the powers-that-be conspire to limit them at every turn. To some extent I see these as strategic poses. We know that in politics 'everyone loves a winner' yet contrariwise everyone 'roots for the underdog'. Presenting yourself as one or the other may help you get the support you desire. However I sometimes get the feeling that they believe their own propaganda.
I was focusing on argumentative conduct rather than issues but the following mindsets underpinning many issues are worth describing too.
* They think that cultures are set-in-stone. A modicum of historic information tells us that cultures change. They bifurcate and fuse and cross-pollinate. Practices originating in one culture transmit to others and nobody has a copyright on them. Links between blood and land are often looser than we think. But for many these things seem timeless and fixed. This makes it difficult for them to cope with a changing world. That may for instance be why even the non-religious can cling to notions like 'marriage between a man and a woman'.
* They think that economics is a zero-sum game. For someone to be well-off they think it necessary for another person to be poorly-off. For someone to benefit they assume others must suffer. They think welfare must necessarily undermine affluence and that the only way prosperity can grow is if the environment is pillaged or more work is done. They overlook the growth potential of services and the monetizing of existing past-times. As a result they obsess over differences in wealth rather than ways of addressing universal human needs. 'Keeping up with the Joneses' and securing what one has becomes a priority. Generosity is neglected as they object to things like improved foreign aid.
There is a sunny side to all this behaviour - it is self-limiting. The stuff I describe betrays a blinkered and rigid mindset. Its expression is more likely to bolster the opinions of those who feel the same way than it is to change the minds of those who are wavering or yet to form opinions. I have a hunch my more constructive and reasoning manner gives a better impression to 'lurkers'. And there is another way in which I think this problem is limited - I find interactions with political rivals in person to be much less characterized by these behaviours. The Internet itself seems to magnify particular ways of thinking while face-to-face interactions dampen that. And in the end those who operate beyond the confines of the Internet are more likely to exercise practical power. Discussion at a polling place is usually far more satisfying than the cold exchanges occurring online - I look forward therefore to the end of this campaign.