To be honest I don't agree with you. Technically I agree and up and downvotes can be used to place good content on top.
However emotionally the same result can be reached with only using the 'positive' upvotes. You find some connection with certain content and upvote it.
When you don't care or you don't think the quality is sufficient you just leave it be, no need to bring it down... You could put some comments to state your opinion.
Imo downvotes should only be used with abusive content or people just exploiting the system.
In short it should be like training a dog. Reward positive behavior and ignore bad :)
Steem is a community and a good social experiment for how a real world community without a centralized authority would operate. When you have people in your community who are bringing down the value and/or abusing your community system, there will be people who stand up and take action for the betterment of all, and there will be those who stand aside.