Some really good points Saikedelix..
I think there are a few reasons people feel the need to share their experiences. You hit the nail on the head with intention of sharing. Like you say, many probably share because they have an innate desire to be understood, as they feel like an outkast in a society that doesn't take this stuff seriously, and mostly deems these experiences 'noise of the brain'. But of course we are talking about things that - in the words of Mckenna - are 'unenglisheable'. Sharing a personal experience in no way guarantees the person listening to have an experience anything like that of your own. Wanting a person to see what you have seen is maybe a little questionable.. as people are on their own journey, at their own pace. That said, with a thoughtful approach, sometimes it may be a good thing to let someone know that DMT exists. From there on, they can always seek out it themselves.
Its important that we check in with ourselves and be aware what effect we may have on someone by sharing this stuff.. we have a duty of care to do those we unveil it to.
I guess the other big reason is that we all see great healing potential with these experiences.. and god knows the planet is in need of that. I see DMT as probably having an important role in that.. but does that mean everybody in the world trying it? Probably not.. as you mention.. there is good reason it has remained somewhat esoteric in cultures that use it. I don't think its an experience everybody need have or should have. Those who are suited for the experience can play their own role in the tribe.. as everybody has their unique thing to bring to the table.
Regarding your point though about discovering it ourselves, and not having it 'put there by someone else' .. at what point do you draw the line though and deem something an external or internal influence? Surely if I am living my life and somebody one day starts talking to me about this or that substance.. that is still part of my journey, and could be seen as merely a different way of the molecule presenting itself to me.
I think it gets a little blurry when thinking about it like this.. but I get it. For example though, I first heard about DMT on Erowid.. there were people behind that site that put the information up - and it was reading people's trip reports that got my attention. In some ways I don't see that scenario as all that different.. its just a different form of delivery. I suppose in that case I had complete freedom to read what I did and didn't want to read though. Going and telling someone about it who didn't ask.. that could be seen as a bit pushy.
I think its safe to say most of us wouldn't have discovered DMT if someone didn't share a degree of their experience. Otherwise how would we end up captivated enough to seek it out?
But its one thing to share our experience with someone and leave them to reflect. Its another thing to then pull out the pipe and invite them back to your house to have the experience you just spoke of. I won't lie - I have done this before. But looking back, it was an insensitive and rushed introduction to something those people would have benefited from taking slower. Fortunately they all had great experiences.. but that could have gone differently.