This is an interesting subject.
I don't disagree with these views, but I think we have to be careful about introducing animals. There are two, related, negative consequences of introducing non-native animals. These both relate to the maintenance of biodiversity.
Firstly, allowing different species which had never bred in the wild to breed as a result of introductions can create havoc with species genetic purity. While many different species will not be willing or able to mate, others will, and it is possible that resulting offspring will be fertile, creating hybrids, which can, over time, negatively impact the original species. Take for example blesbok and bontebok. It is illegal, I believe, to keep them together in South Africa, but I have seen this law ignored. The two will mate and produce fertile offspring. This could have long term negative impacts on both original species, but far greater on bontebok, which are not present in any great numbers.
Giant sable and common sable will also inter-breed, producing fertile offspring. Imagine the consequences for giant sable if common sable were to be introduced into Angola to stimulate trophy hunting there. Giant sable could effectively cease to exist as a species within a few generations.
I don't know if mountain nyala will breed with common nyala (they look much more like a bigger bodied kudu than an nyala), but if they could, bringing them to South Africa could be devastating to the nyala, and vice-versa if nyala were moved to Ethiopia.
Last example is moving zebra around. Many Namibian farms or conservancies have introduced Burchell zebra, which will mate with the Hartmann, resulting in a fertile hybrid. You can often tell when you've shot a zebra that something isn't quite right - the stripe pattern of a Burchell with the dewlap and mane of a Hartmann. I've seen it personally.
Second issue is that an introduced species may do so well that it out-competes indigenous species, which become threatened as a result. Another potential loss for diversity.
There are consequences of messing with nature.
