Many of the questions that I receive begin with "Is it acceptable to believe that..." For example:
Is it acceptable to believe that evolution happened?
Is it acceptable to believe that there was no global flood?
Is it acceptable to believe that the Sages were mistaken on various matters?
Is it acceptable to believe that parts of the Chumash are non-Mosaic in origin?
Is it acceptable to believe that the Lubavitcher Rebbe/ Rabbi Elazar Abuchatzera/ Nir Ben Artzi was/is the Messiah/ a miracle worker/ a charlatan?
My answer to all these questions is identical.
Acceptable according to whom?
According to some people it is acceptable, according to others it is not!
If they are asking whether it is acceptable to God - well, I don't have a direct line. Presumably, if the belief is true, then it is acceptable to Him (but still not to all sectors of Orthodox Jewish society). If it is not true, then it may or may not be acceptable to Him, but people asking me these questions are usually those who already believe these things to be true.
All I can do is to give my own knowledge as to the extent to which these opinions are supported by earlier authorities or conflict with them. But that will not determine whether they are acceptable in any given Jewish community today.
I once published an article in Hakirah which addresses this point, entitled "They Could Say It, We Cannot: Defining the Charge of Heresy." It can be freely downloaded at this link: http://www.hakirah.org/Vol%209%20Slifkin.pdf