I realized that the questionnaire at a normal Q&A site has the most right to choose the best answer, but shouldn't the "best answer" really be the best answer? on the question do people get killed if they leave islam, the best answer has a negative vote while if you scroll down there are other answer with 6 thumbs up and 3 thumbs up, and in my opinion were much better that the "best answer" so shouldn't the community have a little say in what is truly the "best answer?"
The "accepted answer" is not said to be the best answer. It is the answer the author chose as most helpful to them personally. It's just a small way to provide a bit of closure for the original author to say "Thanks, this helped me."
The best answers are determined by the community vote so the best answers rise to the top.
That happens sometimes in the SE format. There is no practical way to choose which is the correct answer. The OP has the freedom to pick the answer that he/she feels is the correct one, and the rest of the community have the freedom to up-vote or down-vote what as they see fit. If someone else stumbles upon the question, he/she are not obligated to deem the accepted answer as the correct one, and may indeed decide that a different answer with a better rating is the right one.