Yes, but did you stop to think WHY you feel a need to down-vote something? You probably disagree with it right? You want to attack it? To de-construct that which is not compatible with your existing ideals? And therein is the proof that down-voting is inherently de-constructive. What if your wrong? What if your part of a majority that is wrong? If the thousands of years which have passed since the invention of Democracy by the Greeks have proven anything, it's that the majority is not always correct, that sometimes like in Pre-WWII Germany, the process of democracy can empower a monster.
By limiting the option to upvoting only, you remove that destructive ability, then the cream of the crop rises to the top not by being resistant to destruction, but instead by simply proving itself to a large enough number of people as worthy of being upvoted.
If you don't agree, then please consider what would of happened if the Wright brothers had to ask the general populace for permission to build their flying machine... they would never of got of the ground, because the majority of people knew, or thought they knew, that the idea was impossible and that it could never work. Their idea would of been massively down-voted and would never of received any funding support, or permission to use the group owned materials.
Additionally anyone who tried to support them in the face of the majority belief that their ideas were bogus, would of faced being labelled as delusional, insane, a troll, a kafir etc etc by various quasi-intellectual members of the group who can't see past the end of their own noses.