A few thoughts.
It is Human nature to take a negative worse than a positive. Negative rep has no set value or price. Bad rep is spent at the value of the spender but received at the value of the receive. Causing people to have issues on the receiving end.
Negative rep is "working" now because of moderation the larger the site becomes the harder it is to moderate the bigger differences you get between moderates etc. Better to remove it now before it becomes a bigger issue later.
To me negative rep is the kind of thing that works as a bunch of mates but as the site grows there are more and more people coming to the site that arnt mates yet. In Australia it is common place for a greeting or getting attention of a friend to be an insulting term "Hey dickhead" for example. However if you use the same language in a larger social group people are going to take offense. You dont get your bosses attention by calling out dickhead across the office at least if you want a job the next day.
As far as positive rep I feel its more like "brownie points". Its a nod to say something is good no matter how significant the good is of the post. A positive unlike a negative is not often an issue if someone takes it too positive.
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