From the very beginning life's purpose has been about obtaining and hording resources, for the purpose of continuation. This can be done in many different ways.
Photosynthesis, chemosynthesis, decomposition, predation, parasitism.
A species will always take the easiest route to the highest cost:reward. Even if a species is kept in check, that's only incentive for one freak mutant to appear. Life is in all essence a lose lose scenario where we either stagnate and regress back into single celled organisms, or keep getting tested and accidentally breed the worst fucking thing you can imagine into existence, something so resilient and efficient and non averted to the mercy, compassion, the humanity that would have gotten it killed otherwise.
https://www.youtube.com/watch?v=plVk4NVIUh8
Now imagine with me, that there are multiple other species somewhere out there who already ran this gauntlet. Can you imagine what came out of it? Do you feel it yet?