I really do think and believe that honesty, absolute, no holds-barred honesty is possible. I don't think it's meant to be had with many people. Actually, I really believe it's only meant to be had on that level with one person: your spouse. If you're single, I'm not sure you're suppose to have it, at least not on all levels, because the physical, sexual component should be missing. I do think it's possible to come close as a single, but it will look differently.
Here's the thing: it's something that you have to be ready for. You have to decide beforehand that you're going to love this person and stick with them regardless, because once you decide that you're going to be honest like that with someone, you open up yourself to the possibility that you can be and probably will be hurt very, very deeply. You give up your right to censor what you find out about, and sometimes what you learn isn't what you wanted to know, and there's no way to "un-know" it. (That could be another good reason not to be this honest with a lot of people. Emotionally, I'm not sure we would be able to handle it.)
On the other hand, it can bring incredible joy and closeness of being known and being loved, that is ultimately a reflection of the desires of our hearts that God perfectly accomplishes in salvation. He fully knows us, and fully loves us. Amazing as it is! And that's why it's necessary in our lives, I think. It's risky, but the potential is huge and hugely important because it might help us come closer to understanding the gospel in ways that few other things will.