Hmm. I'm no INFJ, so my experience might differ from yours, but I'll throw my 2 cents in anyway.
Loneliness and solitude are of course two very different things, and I don't even buy the implied premise that one is the cause of the other.
Solitude is time you take for yourself. You shut out the world to introspect; reflect upon your own thoughts, feelings and experiences, needs, wants and desires, to connect with your own self. It is absolutely essential.
If I don't get enough time alone, I start getting these very misanthropic thoughts. I hate people. Get away from me with your demands on my time and on my being.
Loneliness is feeling disconnected. We think it's feeling disconnected from the world and people around us, but as you can feel lonely in a group or when surrounded by your closest friends, that proves that that isn't really true. No, loneliness is the result of a disconnect with yourself, and from that with the world.
Solitude can actually be the solution to loneliness.
Of course, balance is key. I'm not saying you should lock yourself up and don't interact with anyone for weeks.That's just as detrimental.