Alright, well, if you're talking about having a pure altruistic motive for zoos vs a profit motive then we have to parce this into two separate conversations, one historical (Zoos have their own history and place in culture. The history of zoos profile serious changes in attitude and behavior reflective of changes in the culture at large) and one ideological (Capitalism vs some manner of social altruism).
At present, I would argue there are
zero altruistic pursuits being pursed purely altruistically in our current model of civilization. (Zoos in fact would be the lesser in exploitative practice compared to, say, McDonalds. )
As for part 1 - I think the changes in Zoos and social attitudes about animals are pretty obvious. For some fun, pointed examples of cultural changes we could look at Theodore Roosevelts taxidermy vs Bill Clinton's veganism.
For part 2 - Let's take a brief look at the history exploitative practices by humans in general.
Since human beings discovered we could strap a yoke to an Ox and have it till a farm we have been exploiting one another. A hunter-gatherer, state of nature type society might not be considered exploitative, but those kind of societies are subject to annihilation by diseases and so it looks like you might be forced to choose, at root, between a culture founded on some kind of exploitation (of animals and humans) or a hunter-gatherer existence where all that you love exists on a the knife edge of bacterial destruction. It seems humans have chosen to reject a hunter-gatherer lifestyle whenever an alternative is present. Medicine is largely responsible for that.
To zoom to the present: the phone or laptop you're typing on has batteries built from a cobalt mine where workers are exploited for profit. The university departments where veganism is taught are built on land that was once used as grazing ground for animals, built by workers who likely were paid poorly and got injured on the job.
This brings us back to the exploitative nature of zoos - it seems they fall in line, ethically, with most other institutions and activities in our society. Meaning it's
all deeply compromised if you're going to use foundational exploitation as a cause for judging something as ethically reprehensible.
Onto animals being "subaltern" - voiceless. I think, for example, videos like these are proof that when the animals welfare is taken care of, they respond with love and affection the highest degree they are capable of showing.
Animals are also capable of showing anger.
And I think their behavior at zoos lets the zookeepers and the people around them know how they feel and how they want to be treated.
According to Stanford biology professor Robert Sapolsky, we are also very genetically similar to chimps. I've attached videos he's done that explore the similarities between chimps and humans. I think these similarities indicate that our intuition about what makes them happy are therefore at least somewhat trustworthy.
So now we get, finally, to the motivation behind zoos and why we have them at all. You argued that even if the animals have some capacity to voice their pleasure or displeasure, the motive for their existence, on our end, or seems to be, profit and exhibition based. So, that's not great. But, then again, you're talking about the foundational structure of our society here. How much of that motive do you hang on Zoos, in and of themselves, vs the society they operate in?
And, when we look at the details of how they tend to operate in our society, the profit they generate comes from humans observing the animals. Not eating them or destroying them in any way. If the zookeeper gabes are treating the animals as kindly as they are capable of, that is much better than
most of what we do and have done.
In the Roman coliseum, animals were used for sex shows, were simply killed live in front of people, were forced to fight each other - all for exhibition. In zoos, people who love these animals try to keep them happy and use the fact that they can generate a profit by people coming to see them to keep them alive instead of being eaten or destroyed.
I therefore think it makes sense to to support my G, Zookeeper Gabe, in his vocation.