John,
If the end result is primarily an increase in butterfly species and numbers, a stable population of breeding nightingales and perhaps a safe summer refuge for a few turtle doves, then that surely has to be a positive action, together with an opportunity to monitor progress and learn for the future. I appreciate that some might view this as another well publicised gimmick but we have many instances of "unfamiliar" grazing animals that have been used as a means of natural management, as Deb highlighted, of particular habitats to return or keep them as rich and diverse as they one were. I'm thinking of "flying flocks" in Norfolk such as Konik ponies, Hebridean sheep and I think a type of old fashioned pig similar to Tamworths was trialled in a private wood.
I agree that some reintroductions may be seen as questionable ( eg, WTE on the I.O.W. after North Norfolk fell through a few years back, and Black Storks somewhere ) but why not give it a go. Yes, the continued loss of critical ancient habitat continues unabated but what is there to lose with this scheme?
Regards.