The brahmaviharas, or “sublime attitudes,” are the Buddha’s primary heart teachings—the ones that connect most directly with our desire for true happiness. The term brahmavihara literally means “dwelling place of brahmas.” Brahmas are gods who live in the higher heavens, dwelling in an attitude of unlimited goodwill, unlimited compassion, unlimited empathetic joy, and unlimited equanimity. These unlimited attitudes can be developed from the more limited versions of these emotions that we experience in the human heart.

the absence of a fabricated personality / the absence of conceit means that one is automatically safe and benevolent. that condition of benevolence is not, and cannot be, fabricated or generated. what is commonly meant and caused by a 'metta practice' is the opposite direction from this, because it is an exercise in fabricating feelings, which fabrication must be based on an identity (feelings are conceited by their very nature).

to practice metta that can actually eliminate conceit means thinking about it with a different context. such a practice is an active process of carefully dismantling one's identity, appreciating life's abundance so as not to grasp for further identification, enjoying the peace and ease of being sincerely intent on contentedness, and kindly wishing the best for one's self and others.

"There is the case where an individual keeps pervading the first direction[1] — as well as the second direction, the third, & the fourth — with an awareness imbued with good will. Thus he keeps pervading above, below, & all around, everywhere & in every respect the all-encompassing cosmos with an awareness imbued with good will: abundant, expansive, immeasurable, free from hostility, free from ill will. He savors that, longs for that, finds satisfaction through that. Staying there — fixed on that, dwelling there often, not falling away from that — then when he dies he reappears in conjunction with the devas of Brahma's retinue. The devas of Brahma's retinue, monks, have a life-span of an eon. A run-of-the-mill person having stayed there, having used up all the life-span of those devas, goes to hell, to the animal womb, to the state of the hungry shades. But a disciple of the Blessed One, having stayed there, having used up all the life-span of those devas, is unbound right in that state of being. This, monks, is the difference, this the distinction, this the distinguishing factor, between an educated disciple of the noble ones and an uneducated run-of-the-mill person, when there is a destination, a reappearing.

what is commonly meant and caused by a 'metta practice' is the opposite direction from this, because it is an exercise in fabricating feelings, which fabrication must be based on an identity (feelings are conceited by their very nature).

The fabricated metta seems to be the one that theoretically, according to what is presented in the metta sutta, fuels more rebirth, an identity with an arising and passing 'presence', placed in 'time' and 'space', taking birth again and again, from moment to moment and according to the text mentioned, in a corresponding deva realm.

Always trying to take this attitude of exploration. Use your powers of observation. Use your ingenuity to figure out how things work both in the body and the mind and see how far this process of fabrication can take you. You are not really going to let go of fabrications until you’ve pushed them as far as they can take you. That is what the last tetrad is all about. You begin to realize that the raw material from which you’ve been building these things has its limitations. It can provide only a certain amount of ease but because it’s inconstant that ease is going to wobble. And an ease that wobbles is not necessarily a very comfortable place to be.

Think of a chair with uneven legs, you’re sitting in the chair. You can’t really relax into the chair because the chair might tip over. You've got to stay tense at least a little to maintain your balance. That is the way it is with all the ease and pleasure that comes with anything fabricated. It requires a certain amount of tension to keep your balance.

There will come the point where you ask yourself is it worth. As long as the path hasn’t been fully developed, yes it is worth it. But as these factors get more and more developed you begin to realize this is as far as fabrication can take you. And you begin to lose your taste. You’re feeding on these fabrications, that is where dispassion comes in. You lose your passion for fabricating and because you lose that passion, the process of fabrication begins to fall apart because after all it did depend on factors coming out of the mind, the mind’s hunger for these things, its thirst for these things.

When it’s no longer hungry or thirsty, it just stops. And when it stops, everything else stops. That is where you let go of everything, even the path, even the discernment that got you there. This is how we understand fabrication. This is what insight is all about. Not just watching things arising and passing away but realizing the extent to which the mind causes them to arise and to pass away.

You've got to dig down into this deep level. That is why we work with the breath because the breath goes really deep into your awareness both of the body and of the mind. When you are close to the breath you are close to the sources of fabrication that is where you can see how these things come about. As you manipulate them you get a sense of their range. How far they can go and how far they can’t go.

This is why all of the great meditators of the past where not people who just got really tired of things and got really world weary and just stopped with a sense of depression. That is not how enlightenment is found or awakening is found. They really actively pursue it. How far can you go. What can you do to bring about true happiness. They used their ingenuity, they used the powers of observation. They actively explored. That is what brought them to the edge of fabrication and how they got beyond.

So try and approach the meditation as a process of exploration. You are exploring this process of fabrication in body and in mind. And the breath is a good place to start. A good foundation for your experiments.
http://dhammatalks.org/Archive/110829%20Exploring%20Fabrication.mp3