How To Become A Centaur
There are six types of symbiosis. The type you are referring to is mutualistic symbiosis. As in, mutually beneficial.
Another type, commensalistic symbiosis is where one organism benefits while the other is neither harmed nor helped.
This presents a psychological slipper slope which leads humans to slide from mutualism to commensalism with a shrug. What’s the harm?
The next slippery slope presents itself with the next lower category, parasitic symbiosis. I gain, you lose. If my gain is exponential and your loss is minuscule then I am tempted to go for it.
With two individuals the benefit/harm calculation is easy. Add new variables (ie society) and suddenly we find ourselves (through AIA) encouraging “The Giving Tree” behaviors.