Quite an interesting topic. Eh.. I guess I'll try and overcome semantics with a response that I've not really though through.

I feel like loneliness itself is seldom the root of an issue. I feel like it itself (Loneliness that is) is generally a secondary emotional response to a more direct cause. One is generally not lonely because they are lonely, they are lonely because of a separate condition that causes loneliness.

I think what I'm getting at is it might be first important to question that which causes loneliness rather than first attacking it as a primary cause.

-Alexander Eliot

humans are social animals and our thoughts, values, moral sentiments and bodily emotions depend on social interaction: being friendly or hateful with other people, approving or disapproving someone else's behaviour etc...

When we feel we dont fit in, we feel lonley - stuck in a deeply undesirable state.

that's my finding too, regardless I'm striving for understanding freedom.
please find my thoughts below:

The state of being solitary scares many humans. But only if they aren't lonely at the moment.
In fact, humans are not asocial by design, so the prolonged solitude is rather a choose, and not the fate.
Nevertheless humans mind is confusing most probable reality with imagined, prolonged solitude created by anxiety related to loneliness and unknown.
How it's working?
"I do not want being alone" says herd instinct.
"I do fear of unknown" accompanies mob conformity worm.
"No one wants me" whispers low self-respect worse part of ego.

These three forces support each other and gaining solitude up to the dread level. But a dread is like back seat driver, that causes the worst decisions are taken. Decisions which aim is just conserving by all means the current world, even if it's not worth of that.
The time wasted on observation of prolonged collapse of the world is best time for change, self development, a chance to focus on something, that would rebuild a new, better reality.

Ethical thought;
If we have ourselves to give why should we deny it to someone else?

As I see it, it's a rational instinct, since a lonely human didn't have any purpose, can't reproduce by itself.

I was listening to one of Manly P. Hall's lectures some time back. He made a distinction between being lonely and being alone. think it was about neo-platonism but he might have been drawing this distinction from eastern yogic traditions. The difference is that "the lonely" still crave or need the company of others whereas "the alone" is self-sufficient. There was also the naming of God or Brahma as "The Great Alone" or something like that. I apologize I don't have more information on this at the moment. Google isn't helping me much right now. I'll have to dig up that lecture and listen to it again. Regardless of whether or not I have my references exactly right or not, I think the distinction between "loneliness" and "being alone" is clear enough.

The ethical thoughts of 'the alone" would be more valuable than "the lonely"...maybe?

I agree with Adventavitasinus. For many people loneliness comes as a result of some other action or emotion. A good friend of visited a psychologist only to be announced he was in a state of loneliness. He had limited friends that had disconnected from his life and could not get classes for a fall semester at his nearby community college. Basically he sat at home and did nothing but read, tv and some other non stimulating activities. He claims it was the worst period of his life and it eventually took him into a minor depression. One must be careful though because being alone and loneliness are very different like someone mentioned. Even with social interaction I could see you being lonely still. Let us be clear, with social interaction you must give yourself and receive ones self like an exchange of goods but through social interaction.

Ethical thoughts;
If we have ourselves to give how can we not give it to someone else?

Is it not a reliance on singularity, solidarity and loneliness that is the maker of more criminals?

A crime against nature to be alone?

Is there a right and wrong way to treat nature?

Is nature ultimately inhumane, judgeless, therefore can not be judged by humans?

Is not nature without ethical consideration?

Are ethics and humans un-natural?
or
Are we only un-natural when not naturally ethical?