What DDcorvus already said.
Extinction of species is indeed a part of life. Artifical anthropogenic accerlation of this process, however, isn't.
Less hurt ego, less hubris, please. Species go extinct for various reasons, quite often in correlation with human consumerism. Bickering on a little zoo fan internet forum hasn't wiped out any species so far.
Rhinos are lousy pets:
https://www.youtube.com/watch?v=pA3QfPXVVr8
What you seem to forget in your endorsement for (commercialized) ex-situ conservation is that husbandry changes animals in various, sometimes far-reaching ways. By eliminating external pressures such as predators, parasites, hunger, competition for food/mates etc. while introducing others (constant contact to humans, food replacement, different climates etc.), we change the animals in our care. Sometimes subtly, sometimes with ostentation (colour morphs, for example). More or less unwillingly, we domesticate, allowing "the runts of the litters" to reproduce.
Let me illustrate this to you by a simple example: let's say we catch 15 specimens of an endangered species of gazelle from the wild to establish an ex-situ founding population. During capture, five animals die due to stress of capture, traumatic injuries etc. In the introduction and establishment period, another five die due to various reasons (diseases, age, stress, injuries, miscarriages, intraspecific aggression, malnutrition etc.). In the end, we have five specimens that seem to have settled well and maybe even start to breed steadily. But are these the specimens that will provide optimal offspring for future reintroductions? Or have we (unwillingly) seeded out the most skittish (not the worst attitude when you're preyed upon in the wild) and are now keeping and reproducing animals that are calmer and thus better suited for captivity, yet not consequently for reintroduction? Unfortunately, our scenario ends as our gazelles contract paratuberculosis from a group of closeby kept goats and can therefore never be reintroduced. Interspecific disease transfer is still quite an issue in ex-situ husbandries, in particular in zoos.
So is ex-situ breeding always a bad thing? No. Depending on the species and situation, it has its merits (very often in collaboration with experienced private breeders). It's just not an universal cure-all.