The slogan of “Elu Ve’elu” has conquered all. But there are plenty of cases where one or both sides are just wrong. When it comes to reality, for instance, if my position is based on a true conception of reality and yours on a false one, you lose.
This is true for the “debate” on women’s wigs (see here part one, p. 7). If the Heter is conditional upon claiming a fact which just isn’t so (e.g., wigs don’t have the same effect as hair), the legal ruling doesn’t stand at all. This is true for lighting the Chanuka Menorah in a fake “chatzer”, which really is not part of the same property (“reshus”).
And it’s true for “Kesem Kegris” as well. And yet, Rabbi Nissim Karelitz, with no shame, writes one may not even be stringent (Chut Shani on Niddah p. 155):
ואין לו להפקיע שיעבודו מאשתו
This appears to be a Reddish Herring.