Opinions in arguments that are not leShem shemayim are not included. Almost all of the sources (which I know about) which comment on this issue do so in the context of halakhic arguments. (R' Kook is the exception.)
R' Kook (אורות הקודש) seems to hold that in theory, everything is included, but in practice, we only accept "acceptable" opinions that follow "preestablished standards."
R' Moshe Feinstein (אגרות משה - הקדמה) also makes a distinction between practical truth and theoretical truth.
Rashi (Ketubot 57a) holds that factual arguments, such as whether Rabbi A said something was assur or muttar, are not included, for there is a definite truth - he either said "assur" or "muttar," but not both. But general arguments in halacha are included, for something could be assur in one case, but muttar in a different case.
According to the Ran, even the incorrect halakhic opinions were given at Har Sinai.
Also note that the Gemara (Sanhedrin 17a) says that one of the tests for someone to be gain a seat in the Sanhedrin was whether he could be מטהר a שרץ מן התורה, possibly implying that even obviously false opinions are valid.