Anyway, the question I wanted to explore is if the fixed karma threshold for downvoting (100, IIRC) does not risk becoming a problem when a larger population (and less active on average) becomes able to manifest disagreement this way or if the threshold should be a function of the average karma of the active population.
i think the better point to be made is that people downvote opinions that they don't agree with (as opposed to downvoting something factually inaccurate or bad in some other way). its good to have different points of view, and if people get punished for expressing the unpopular one, fewer people will express them.