You mean like people who believe they can solve any problem by just deducing the solution from first-principles without even trying to find some prior art (I know the author of that post didn't, because it took me all of five minutes of googling to find plenty of it)? Or people who believe there are easy answers because they are just unaware of the the complexities of the world and so maintain a simple, solvable, model of it in their minds? Or worse, people who justify their views with the naturalistic fallacy and say, "well, this is how the world works; we can't change it so we might as well make the best of a shitty situation"? (as long as they don't get the short end of the stick, of course)
And you need to understand that people who write articles like that are being dismissive towards real people who have actually dedicated their lives to studying social problems (or debating questions of ethics).
> but have made zero attempt in educating him
Because the issue is very, very complex. I have provided a link that points to where to get started when approaching this difficult topic.
> if i was in a desert and somebody is really thirsty, why is it unethical for me to sell him some water?
The reason you're bringing this up is because you think that the analogy is apt, but I'm not so sure. There are some ways to approach this (which are far from comprehensive).
First, you need to explain the situation. How much water do you have? Let's suppose you have a supply for a million people. I would say that in that situation it may be ethical for you to sell that man some water, but if you do (rather than just give him the water), you now have a certain obligation towards him. For example, to make sure that he has enough water. Another question is why is that man in the desert in the first place? Could you have possibly contributed to his being there, or did not do enough to stop him? Suppose that the reason he is there is because he got lost, and he got lost because the map of the area is wrong. And it's not just him, but many people get lost because of that map, and that is precisely why you've decided to get a water tanker and set up shop in the desert. Now, it may not have been in your power to change the map, but if you had made the same effort into getting the map fixed as into setting up your water stand, there may have been a good chance that it would have been fixed. So now this puts you in a different role: you're not trying to help solve the desert problem, but you're benefiting from it not being fixed, and while you may not have been able to fix it yourself, you could have helped but you didn't. If that is the case, I think that you have quite a strong moral responsibility towards those poor souls. You are not to blame for their problem, you certainly didn't make the desert or the wrong map, but you're not really trying to fix the cause and you are benefiting from it. In that case, I would say that at the very least you have the moral responsibility to sell the water at a very decent price, and to make sure all your lost customers make it out alive.
My point is that mutually-beneficial exploitation has been known to be a very hard problem for a long time, and so we try to approach it on a case-by-case basis, and make sure we try to understand the full ethical picture. Simplified analogies don't help -- they remove nuance from a very nuanced question.