1) Good content, you like it, you upvote it.
2) Bad content, harmful, misleading, downvote it.
3) Good or ok content, you dont like it, you do NOT downvote it.
The 3th point is most importand. You have right do disagree with someone as someone has right to express his opinion. As long as its not harmful or abusive, you do NOT touch it.
Voting systems create incentives, people's behavior is shaped by incentives.
If a voting system allows manipulating conversations (for example by influencing where a post appears and therefore how many people see it), people who benefit from manipulating the conversation will do so.
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EDIT: Also, if you think it's an N-state system, it should have N+1 states because the default is "didn't read / don't care". Apart from this state, there are at least 2 important axes: 1) factually correct / incorrect 2) agree / disagree.
What makes your way correct and other people wrong?