I love and appreciate them!
It's
great to have animals on hand that kids (And guests in general, really) can actually
touch and otherwise physically interact with. I echo previous users who pointed out that more than a few modern day children have limited opportunities to socialize with animals, especially those that
aren't commonly kept pet species like the dog or cat.
Plus, a petting zoo exhibit doesn't necessarily
need to consist of just farm animals! Relatively docile exotic species can work just as well! Think Patagonian maras, Capybaras, Kangaroos, Wallabies, Emus, Parrots, Fallow Deer, Porcupines, Camels, Ostriches, Water Buffalo, Guineafowl, Muntjacs, Ring-tailed Lemurs, Tortoises...
One place nearby where I live even has species like Bison, Yak, Zebra, and even baby
Alligators!
That being said, an exotic petting zoo exhibit would probably require significantly more management to assure guest and animal safety. In light of what, it's easy to understand why many zoos opt for farm animals.
My only quibble with most farm-themed exhibits is that they typically feature
common breeds of livestock. Instead of
rare or historical breeds of livestock. Most of which currently suffer from limited interest and low numbers. Just take a look at what breeds The Livestock Conservancy spotlights:
Home - The Livestock Conservancy
Choosing to house (Or even better,
breed) rare breeds of livestock should go hand-in-hand with zoos IMHO. Fits
perfectly with the messages of education and conservation that the vast majority of zoos promote nowadays.