This question already has an answer here:
Down voting an answer is a privilege given to users who have at least 125 reputation points.
I am requesting for a feature to prevent users from down voting (other) answers to the question, as soon as the user gives his/her own answer to the question.
As a follow up, a user who has down voted an answer to a question, the user shall then be labelled as a referee, and his/her privilege to give an answer shall get revoked.
Optionally, the user may be given the option to sacrifice his/her down votes to answers in that question, for the sake of giving his/her own answer to the question.
Users are generally able to be objective while giving up and down votes, provided they have given an answer to a question. As soon as they give an answer, however, they more or less lose their objectiveness. While a user would definitely not vote an answer other than his/hers up for having lost objectiveness; this is not the case for voting down...
A user may vote an answer down, simply because it is not theirs. <<< this is the tl; dr
I think we would all agree that in any sports, it wouldn't be appropriate to let a player be a referee. We don't allow this for up-votes, by disallowing casting up-votes for our own answers; and this suggestion/request asks one for the down-vote counterpart.