Tl;dr:
- In Theory: Yes
- In Practice: No
In Theory
In theory, as we know, posts should be voted according to their quality so that visitors can find the best ones easily.
So, when some answers are provided to a question, the best ones should be placed at the top of the answer list to help readers of the thread find more useful answers.
However, the questioner may accept some answer according to their need and understanding of the subject of the post; it is clear that such a choice does not necessarily indicate the best answer.
Thus, in theory, I agree that accepted answers should be unpinned.
In Practice
In practice, as we know well, poster are often voted, not their posts. Let us recall the following community normcommunity misbehavior concerning the issue:
Questions are illigiitmately upvoted for reasons unrelated to the quality of a question. A very poor post answered by 5 separate users may very well get five upvotes. Friends upvote friends, admire certain users, etc.
(Although this a harsh but irrefutable fact, I think ignoring/evading it would not help us to find the best solutions for our community at all.)
Although such abuse may happen in acceptance of answers, its occurrence rate is likely much lower than that of post voting.
So, not to mislead people, especially novice users, it is strongly recommended not to implement the feature request until some people change their behavior.