Rav Schachter - the posek for ORA - provides a cogent discussion of the pitfalls of using mekach taus to free an aguna.
It is important to keep in mind that Rav Moshe Feinstein clearly states that the negative condition must be preexisting and so severe that no reasonable person would tolerate it - and the spouse must leave immediately upon discovering it. In addition a psak of mekach taus based entirely upon negative reports from the wife - without the husband being directly evaulated by a neutral expert therapist - is clearly invalid and indicative of biased poskim.
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Making a Farce of the Halacha
Torah Web.org The Ramban writes (in the introduction to his
sefer Milchamos Hashem)
that the study of Talmud is not like mathematics. In Talmud study, a
halachic analysis is not a geometric proof and its validity need not be
contingent upon accurate application of hard logic to unassailable
axioms; nor is a halachic analysis deemed invalid only upon
demonstration of incontrovertible logical errors or fallacious
assumptions. What is significant in halacha is the approval or
disapproval of halachic experts, implying the
reasonableness or
unreasonableness of the argument. One must have a strong tradition in
psak halacha (rendering of legal decisions) or one can float so far off as to develop the most ridiculous ideas, all in the name of halacha.
The Torah prescribes the divorce procedure such that
the husband must participate voluntarily. When he refuses to
participate, his wife has no other means to be free of her husband, and
while she remains legally married to him she may not marry another man.
This situation, though unfair and tragic for the wife, is essentially
the creation of a man who has shown himself to be an evil criminal, and
is abusing his wife in this contemptible way. He has made her a virtual agunah
as the husband alone has the authority to free her. Over the many years
of our history the rabbis have done whatever they could for any woman
so trapped in this lamentable predicament. Unfortunately, no categorical
or general solution to the problem emerged.
About forty years ago an Orthodox individual proposed
a solution. He reasoned that the woman requires a divorce only if she
is married. Although annulment is not an option, it may be possible to
find cause to invalidate her marriage by finding a fatal flaw in her
wedding. For example, the wedding requires that the groom give the bride
an object of sufficient value, one that the groom is entitled to give,
while declaring his intent to thereby marry her, without deceit in any
of the particulars, all under the watchful eyes of legitimate witnesses.
If any of these conditions are not met then the wedding is fatally
flawed. Likewise, if the bride or groom deceives the other in a material
way, the other may legitimately claim that the entire wedding was under
false pretenses and thus void. Thinking along these lines, the
individual referred to above argues that if the bride and groom had
realized that their personalities were incompatible, they would never
have agreed to get married. Hence, the marriage was effected in error,
lacking the requisite da'as (awareness) for a wedding, and no Get
is needed to separate them because they were never married. At the
time, Rav Yosef Dov Soloveitchik declared this suggestion ridiculous. As
the years went by, the ridiculous has become the sublime. [...]
To declare a marriage a kiddushei ta'us because the wife didn't
realize that the husband would be unsuccessful in holding down a job and
earning a living is simply unacceptable. To invalidate a kiddushin due to ta'us the halacha requires an extraordinary mum gadol (very significant defect), with a very obvious umdana d'muchach (compelling assumption) that no reasonable woman would agree to marry such a man (see Teshuvos Beis Halevi, vol. 3, pg. 23). [...]
Moreover, even in the case of a sale that was canceled because of a mum, the Rambam wrote (Mechira 15:3) that if the purchaser continued to use the item after having discovered the mum, he cannot later claim mekach taus. Continued use of the item indicates that the level of the ta'us
is insufficient to warrant voiding the transaction. Likewise, it is
transmitted in the name of Hagaon Rav Moshe Feinstein zt"l, that even in
the rare case of an unusual mum gadol, through which the wife would be able to remarry without a get because of the ta'us on her part at the time of the wedding, if the woman didn't walk away from the marriage immediately upon discovering the mum, the halacha of ta'us cannot be applied.
Rabbi Eliyahu Ben Chaim (Yeshivas Rabbeinu Yitzchak Elchanan) published an essay in the Yeshiva publication, Beis Yitzchak (5758), explaining the mistakes of these "batei din", and cautioning the agunot not to rely on such meaningless "heterim". In his essay he quotes Chacham Ovadia Yosef as having said the same.
It certainly is a great mitzva to help an aguna escape her plight, but issuing a heter nissuin (permission to get married) to a woman along the lines of heter nedarim is simply a farce. Let us not make a joke out of the Halacha.