Primitive men weren't stoic. We attribute that quality to them because we now understand how common diseases work and why they were so prominent in that time. That understanding -part of the advantages of modern life- has forever changed our perspective on the subject.
For primitive men, life was probably terrifying and a constant struggle. When someone in the tribe got sick, they didn't say "oh well, that's life! What can you do?". They'd attribute it to some supernatural force that was clearly angry at them for something they did. That's why they created various superstitions and rituals, as a way to combat the things they could not understand and control. That's not exactly being stoic.
That being said, I do believe that some people are not equipped to deal with modern life, and that a larger degree of solitude is part of that life.
I'm lucky in the sense that, for me, being alone does not have an emotional tax. I enjoy being alone as much as I enjoy being in good company (and because you cannot always count on the company to be good, i'd say I enjoy it even more). I'm not saying I like to be alone sometimes. I really enjoy being alone for extended periods of time and could imagine living the rest of my life alone to some degree (I do like the rhythm of modern cities). But I understand the frustration of those who cannot endure solitude or get a feeling of loneliness from it.
I wouldn't say modern society sucks, though. It has a lot going for it, but it's obviously not perfect.