You're missing the point. Exercise would serve to improve both physical and mental health. There is a reason it's practised. Take Tai chi chuan for example.
Honestly, it's been a long time since I've met anybody as cynical and hopeless. You've obviously been beaten down for so long that you've convinced yourself that every human being is evil and the world is a terrible place. Guess what, it isn't so. We as a species are indeed quite a sadistic bunch, but the world is not this doom and gloom picture you've painted in your mind.
Yes, unemployment is high these days. Graduates are having troubles finding jobs. Wages suck and there is no security. The reason? It's the simple ebb and flow of society. Every generation has a recession or general economic downturn.
Find whatever the core of your problems is and fix it. Why are you depressed, why are you poor, why are you alone. Instead of spending your days immersing in self loathing and discussing it online to obtain anonymous pity, you could devote some of it to improving your situation.
Mind you, I'm not trying to put you down. I was in the exact same situation a few years ago, spending at least 6 years virtually alone after experiencing some traumatic stuff. It was only when an anonymous doppelgänger said "I fixed myself after realizing sitting alone and talking about it online wasn't going to fix anything."