Circumcision for the dead

If I were to learn that under the direction of a rabbi someone circumcised a volunteer for and in behalf of one of my ancestors, would I be offended? Would I think that the memory of my ancestor had been dishonored?

Not at all. I would be delighted to know that my Jewish brethren were so concerned with the welfare of my ancestors that they would make this sacrifice of time and, ah, effort. I don't think it would do my ancestors any good, but that would make no difference to me.

So, why do some Jewish people get upset when they learn that the Mormons have baptized someone for and in behalf of a departed Jew? Why should anyone be upset for any baptism for the dead?