Broken down into the few issues that arose in the course of this thread:
1. It's... INCONSISTENT D: ! You know what ? I'm not autistic. I'm willing to accept that the world is inconsistent. That's one of the most basic facts of life, to be honest.
Furthemore - as my ontology lecturer once said: "Anyone who thinks their views are 100% coherent is incredibly naive". I'm willing to live with this too, as long as things appear quite reasonable on the surface.
2. Down with down-voting ! Yeah, that's a great idea. After all - if people can no longer downvote others, everyone will love everyone else and this place will blossom into universal positivity ^^ !
Well, no. Guess what, genius, people will most likely think the same things but will merely be unable to express them in the gentlest slap-on-the-wrist way we have at out disposal.
This is how I imagine a forum full of up-votes only. Magnificent, isn't it ? 3. Let's imagine... OK, let's say that the forum does away the minus sign. All it takes is a little aggrement among us dissenters to treat the + button as the - button and pretend the + no longer exists (never mind the logistics, just follow the thought experiment along. The conclusions don't necessitate the premises). Soon enough green-marked posts would be the ones stigmatized and people would quickly grow to understand this practice and interpret the forum accordingly.
4. The dumbest thing about the entire suggestion... ...is that it perceives the symptoms as the sickness. People don't downvote others because there is a button there. They do so because THEY SEE IT AS JUST.
Can the community be mistaken and misjudge the rating a post should receive ? Duh. Does non-zero fallibility mean we should get rid of the system entirely ?
Hilariously enough - this forum rarely does treat people unfairly. Most here err on the side of caution.
5. Who gets downvotes This is somewhat beside the point but I'm going to mention this anyway: how can we tell whether something we are about to post is OK ? Guess what - it's not an algorithm we follow. It's not a set of posted rules. If there's one thing I remember from my ethics lectures, it's that there can never be a finite set of rules an individual is meant to follow (and even if there is, it far exceeds the ability to remember, comprehend, calculate in real-time, etc); any ethically mature individual should know that and still be able to mostly make the right calls when faced with real-life problems.
In other words - use COMMON SENSE. People who are able to figure out the appropriate things to say in RL conversations should not lose this talent once online.
What makes the fact, that a post should be down-voted, a dead-giveaway ? As rule of thumb - the poster sounding like a blowhard or an idiot to use less than profound terms. Both cannot be reasoned with yet should not be simply tolerated (with possible exceptions - see above).