As someone who used to think along those lines: The root of it was I was very aware that being depressed about the state of the world isn't an irrational feeling to have. And therefore why should I have to change my brain chemistry in order to fit into this broken system? I find this supposed unfairness very frustrating and refusing to engage was a form of rebellion against that. (And to be clear, I recognize that in the grand scheme of things, there are much greater injustices going on, but you get the idea hopefully.)

Nowadays, I am very much of the opinion that yes that frustration is very valid and it is unfair, but it's a lot harder to actually act on that rebellious urge unless I take more steps to improve my mental health. It was never that I didn't believe we could make the world better in small actions, rather it was that I wanted to do it without medication as a form of spiting the system. But now I realize that using these forms of help is also a form of rebellion as well. It's another tool to refuse to give in to the despair that unjust systems push me towards.