Yes, again, I just have to iterate...look to the audience. In every audience you'll have a range of desires, backgrounds, knowledge, experiences, and prejudices. For me, I'm a designer with nearly 2 decades of experience studying audiences and zoos (including my time in school), and I personally still get an absolute high from a silly thing like giving a giraffe a piece of lettuce. It works for me. But it may not work for everyone. A passive experience with lots of educational aspects immersed in the wild of a zoo may work for others. But its not going to work for all. Most designers and zoos go for the 'what's gonna work for the most' approach since as Zooplantman points out, money is limited. And it has been shown, through scientific studies, that zoos do affect conservation attitudes--people DO learn and appreciate nature more for their visit. So even though maybe people aren't running out and sacrificing some major part of themselves for conservation, we are making incremental strides.
Also, as far as interactions go, animals are not forced to do it. Their meals are not withheld. They choose to participate. And I know of at least one study that indicates that feeding experiences are actually beneficial to the animal. It reduces stereotypical behavior by adding a simulated foraging experience and of course, believe it or not, interacting with the public is actually very stimulating for animals. Would it feel less dirty if people didn't pay for the experience?
I also question the statement that just because moms and dads are more concerned about whether or not Junior is having fun during an interaction means they are not affected positively. There are 5 segments of our audience: Experience seekers, spiritual pilgrims (which I can tell many of you on here are these!), professionals, explorers, and facilitators. The facilitators are the concerned mommy and daddy. Are we not meeting their needs by providing experiences that bring joy to their kids? If we meet their needs, they will continue to come back, and continue to experience and learn (and expose the children to learning). Its really really really hard to get the attention of parents at zoos...they are spending their time wrangling children and driving strollers, so if they have a moment where they feel proud as a parent--something that they feel is important enough to actually get out the camera then share with their friends online, I feel like that's a pretty big achievement.
On another note, all AZA accredited zoos contribute to conservation with monetary giving. Whether or not they are doing so by utilizing a specific experience or by a segment of their annual operating budget, it is being done. And many are leading conservation programs themselves.