The difficulty with Cooper's hyperbole is it misses two points concerning the LDS practice.
First, criticism of LDS' rebranding of the deceased's souls is analogous to apologists for Tony Blair or Barack Obama criticising David Icke for stealing their humanity by asserting that they are, contrary to all appearances, actually 10-foot intergalactic reptilians. I assume Cooper shares my conviction that LDS are not actually empowered with the supernatural custodianship of all humanity's souls and that baptism by proxy is when all is said and done – and with all respect – objectively speaking complete bunkum. So, what precisely is the concern? That Rabbi Cooper could be wrong and Mormonism right? I doubt it.
The LDS have a host of practices that are just plain weird to all external observers but, let's face it, so do most other faiths. For example, the Santerians have the rite of Bembe in which they 'mount the head' and become possessed of animistic spirits and dance, and Christians eat the very body and blood of a man who died centuries previously. Each of the practices reasonable to their participants often look strange or even objectionable to observers (apart from atheists, of course, who are in the privileged position of viewing us all with incredulity!) The call of Cooper to exclude those of Jewish faith from the LDS baptisms amounts to a call to limit the LDS' offer of salvation to all the peoples of the earth except those of Jewish faith.
That the majority of people do not believe in this LDS God and consider the baptism a waste of good water does not change the fact that such internal theology has the potential to purvey hateful practise. It is only recently that LDS have turned away from their racist theology that denied the priesthood to followers on the basis of race and they have made genuine improvements in this regard; why turn the clock back to a time when salvation is, again, limited by race and creed? We have seen that happen before and I have no desire to see it repeated, however well-intentioned the call may be on Cooper's part.
The case of the Catholic church is instructive here. Cardinal Ratzinger (now Pope Benedict XVI) felt the need to formalise what we all know instinctively, namely the fact that an LDS baptism is not personally valid if one is not a LDS member. With that blindingly obvious conclusion in place the Catholic church has refused to cooperate with the LDS-sponsored genealogical research, with the result that Catholic records are not passed on. What the Catholic church has not done however is to accuse the LDS of denying the Catholicism of those who have been baptised after their death – which is precisely the charge levelled by Cooper.