This does not appear to be a question and as such should probably have been filed at http://bugs.askbot.org/ or suggested via one of the mechanisms here http://fedoraproject.org/wiki/Ask_fedora.
On a more personal note the point of systems like these is that "bad" answers will be downvoted, "good" answers will be upvoted, and "excellent" answers - ideally - will be selected by the person who asked the question as their favourite one. That does not however mean that those downvoted posts are not an important part of the record and should be erased.
I would question why we need the inverse of the 'tick mark', the tick mark already highlights which answer the original poster thought was "most correct". Implicitly all other answers were considered "less correct" or "wrong" and the community will organize them appropriately on merit.
Looking at the people page I think part of the problem right now is that there are only ~10 users with enough karma to downvote answers, I would expect as we get more users in this category this problem will go away as it will be clearer which answers are excellent/good/bad. You will find that if this site garners enough users then this will occur very quickly (for reference there are another 10 users who are very close to reaching this threshold already since I wrote my original answer), as it has on similar sites, if it doesn't garner enough users then no amount of "features" like this one will save it.
Please use the "meta" tag when filing feature requests. It makes it easier for the admins.
You don't have to edit to do that. just retag and press enter twice.