I suspect that the OP confuses “majority” for “average.”
I see this after elections every once in a while: candidate A gets 60% of the votes (of those people who bothered to stop by a voting booth on the correct day) and suddenly the “landslide victory” gets translated into “everybody” voted for him or her. The reality might be that closer to 50% of the people did not prefer him or her, but that too many were too lazy to vote–and even using the actual vote tally, four people out of ten were in opposition.
I suspect that among Dopers, a slight majority who choose to post on those issues tend to favor left-leaning social policies, right-leaning economic policies, tend to oppose the death penalty, and tend to accept private gun ownership. (And, of course, even this categorization is skewed by failing to consider a strong Libertarian element among Dopers that makes a hash of the “Left” and “Right” dichotomy.)
Beyond that, there are a number of issues that can cloud the perceptions of people when making charts. The late Collounsbury was routinely lumped in with the “Left” when posters were whining about the board leaning too much to the Left ort Right in the Pit, yet he was quite clearly an old-line Conservative in economic matters and would have been much more at home with the Moderate Republicans than the Democrats (if the Republican Party had not amputated their Moderate or Progressive wing). His staunch opposition to the Neo-Con political perspective placed him at odds with a number of posters on the Right and he got branded “Left” by default.
The use of “average” (whether it be calculated as a mean, median, or mode average) gives the false impression that “everybody” shares some belief or understanding, when the reality in a place like the SDMB is that most posters on most* issues find themselves in one of several competing camps with a slight majority appearing to favor one or another position.
There are issues on which an overwhelming number of posters tend to agree (with still a lot of disagreement on the details): homosexuality is generally regarded as an innate orientation, not a moral choice, for example, to a much greater degree than one would find in the general U.S. population. Evolution has a much greeater acceptance as a scientific reality on the SDMB than one would find in the general population. Abortion is a issue where I suspect that the numbers are closer to 50-50* than to 95-5, but most people would prefer to simply avoid a topic that gets rancorous so quickly on the grounds that there is little point in raising one’s blood pressure or potentially alienating one’s on-line friends where there is almost no chance that one will persuade them to change their opinions.
** (I am not claiming an actual 50-50 split. The numbers could easily be 60-40 or 80-20 or something else. I am only pointing out that a reading of the board might give a 95-5 impression and that I suspect the numbers are closer to an even split than that.)