MinggI am very interesting in seeing how this system works. My initial thoughts are as follows. 1st example is my interpretation of how downvotes play a role(in theory). 2nd example is a potential flaw? Maybe a potential strength? Not really sure.
For example #1 - I see a video with tons of upvotes but I genuinely dislike said video. It's bad sking, music, offensive, whatever the reason. Your only choice is to not vote which doesn't have a negative impact on the video. Now, of course a bad video won't get as much attention and thus will not be as promoted as a good video. However, you as the downvoter/disliker have no way to really vote. With downvotes, they hurt the video in terms of its rankings and what not which is reflective of the person who downvotes's honest opinion.
#2 an actually shitty piece of media getting only upvotes with no way to downvote. A bad edit obviously won't attract the same attention as a good edit but there is the possibility of upvotes. I'll use 5 upvotes as an example - you could get 5 genuine upvotes from friends without breaking rules or abusing the system. This scenario has the potential to equate to an edit that "gets lost" in the mix - maybe uploaded at a weird time or a ton of other edits are uploaded at the same time and it gets over looked. That "good" edit gets 5 genuine upvotes for being good content, but still it is "equal" to the shitty edit with friends' upvotes and there is no way to really rank them. At least with downvotes, you could actually determine that people don't like this vs. people haven't seen in/voted. If that makes sense?
So the algorithms which run against this are quite advanced. Really, in all instances it takes into account what the opinion of site visitors are, and actually casts out the outliers of downvotes. Same with your scenario - it corrects for small amounts of upvotes and ranks things with confidence above others.
However - even though I've explained this fact a bazillion times over, people still upload a piece of media and go and downvote all the other really good stuff to benefit themselves. This makes media contributors mad, and they go and upload to Instagram and ditch Newschoolers.
In the end of the day, the algorithms take care of this and what you actually want will happen. Good stuff will rise up, bad stuff will fall away. If you really want to hate on a piece of media, leave a comment. :)