The agree/disagree button gives people an easy way of expressing disagreement. If they have no such easy way, many will downvote instead.
When that happens, the quality control aspect of the voting system is severely impaired. All posts for positions that most LW readers disagree with would have a de facto handicap, since they would get many negative votes that they should not have gotten based on quality.
I somewhat suspect though that even with a disagree button, voting down will sometimes be used to express disagreement, just because its effect is more visible and of more consequence. In this respect, I think that a agree/disagree system will be effective to the extent that it has real noticeable effects (just as karma has a real effect in terms of granting privileges and conveying virtual status). If all it does is change a number attached to the comment, I think people will still succumb to abusing downvoting, albeit much less frequently than presently.
The agree/disagree button gives people an easy way of expressing disagreement. If they have no such easy way, many will downvote instead.
When that happens, the quality control aspect of the voting system is severely impaired. All posts for positions that most LW readers disagree with would have a de facto handicap, since they would get many negative votes that they should not have gotten based on quality.
I somewhat suspect though that even with a disagree button, voting down will sometimes be used to express disagreement, just because its effect is more visible and of more consequence. In this respect, I think that a agree/disagree system will be effective to the extent that it has real noticeable effects (just as karma has a real effect in terms of granting privileges and conveying virtual status). If all it does is change a number attached to the comment, I think people will still succumb to abusing downvoting, albeit much less frequently than presently.