(Sincere question and playing a bit of a Devil's Advocate here, but I keep running into this question and feel that I have to ask it:)
I only have a lay person's grasp of Theravada, but from what I've read, Shakyamuni taught that there is no soul or individual personal entity to begin with; and even much less of a one regarding rebirth.
That is, first you're nothing, a mere illusion, and then the patterns that "I" created will ripple through time to create a "reasonable facsimile" of "me" in some karmically-designated "format"; a format that only resembles me, but will not be me.
I have, however, an instinctual intuition that my view of this issue must be wrong - my understanding must be incomplete or misinterpretive, because:
1) If I'm illusion, why should I practice right action and compassion toward myself? I'm just a temporary cipher composed of impermanent processes, which at death will be scattered anyway. So - 'Why Bother?"
2) Ditto re: other sentient (non-) beings: why should I regard them any more highly or with any more reality than I regard myself? Like me, they are all illusions, empty of form/self-nature, temporary ciphers; how can a non-being spiritually assist or obstruct another non-being? So again the question - "Why Bother?"
3) Ditto re: "my" rebirth:
First, that rebirth won't be me or "of" me. Rather, it will be the emergence of just one more mere cipher, a carrier of my ripples (karmic burden), but it won't be me, so why bother?
Second, why should I try to "get off the Wheel" if I'm not really on the Wheel to begin with? I'm just a temporary, impermanent heap of skandhas - no me; no birth-death-rebirth of "me", and putatively no Wheel (because I don't really exist, the Wheel or Cycle of birth-rebirth is irrelevant). So - why bother?
Third, why should I try to ease the sufferings of a complete stranger - i.e., the future "me" - "my" rebirth pattern? Why should he or she enjoy the fruits of my store of merit or suffer my karmic debt? I owe this future "person" nothing.
If I am no-self, so too will my rebirth pattern be no-self, just another pointless gust of empty wind.
I could see expending effort toward an "auspicious rebirth" of MYSELF as a human being who will benefit from my previous lifetimes of merit and Dharma-knowledge. But that's exactly what Shakyamuni denied. There can be NO rebirth of "ME" ... and thus a meritorious Dharma-led life NOW furnishes me with NOTHING later on.
So, again - why bother? What's the point?
If hatred or compassion is merely a game between two or more ciphers, no-selves, then what's the point? What's in it (Buddhistic self-denial, learning the Dharma, facilitating a "good" rebirth) if Anatta is the central fact of our (illusory) lives?
Bluntly put: what's in it for us?
To sum it up: Painted rice cakes don't satisfy hunger.
You practise because you feel a need to be profoundly and truly happy and intuit that Buddhism is a way to get there. And that is all there is to it.
All these speculations about how the landscape might look to you once you get there is just so much prapanca. The implications of all this will sort itself out on its own accord in ways you quite literally can not imagine, simply because you don't have the experiential framework to do so. It's like imagining what a foreign country is like, how it smells, whether the people are friendly and the food is good and so forth by reading the entry in the CIA World Fact Book. It's not a question of how close to the mark your speculations might be. It's not even close to putting together a proper picture.
If you feel a need to answer questions about why you should bother helping future selves, other beings, etc. I suggest a philosophy course for your intellectual needs. Part of the awakening process involves becoming the kind of person who delights in giving freely to others in such a way and finds great happiness in benefiting themselves, their future 'selves' and all beings equally. If you want to awaken, one can not expect to take in expansiveness of the sky by looking through a pipe.
MN63: Cula-Malunkyovada Sutta wrote:
"It's just as if a man were wounded with an arrow thickly smeared with poison.
His friends & companions, kinsmen & relatives would provide him with a surgeon, and the man would say, 'I won't have this arrow removed until I know whether the man who wounded me was a noble warrior, a brahman, a merchant, or a worker.'
He would say, 'I won't have this arrow removed until I know the given name & clan name of the man who wounded me... until I know whether he was tall, medium, or short... until I know whether he was dark, ruddy-brown, or golden-colored... until I know his home village, town, or city... until I know whether the bow with which I was wounded was a long bow or a crossbow... until I know whether the bowstring with which I was wounded was fiber, bamboo threads, sinew, hemp, or bark... until I know whether the shaft with which I was wounded was wild or cultivated... until I know whether the feathers of the shaft with which I was wounded were those of a vulture, a stork, a hawk, a peacock, or another bird... until I know whether the shaft with which I was wounded was bound with the sinew of an ox, a water buffalo, a langur, or a monkey.'
He would say, 'I won't have this arrow removed until I know whether the shaft with which I was wounded was that of a common arrow, a curved arrow, a barbed, a calf-toothed, or an oleander arrow.' The man would die and those things would still remain unknown to him.
MN2: Sabbasava Sutta wrote:
"There is the case where an uninstructed, run-of-the-mill person... does not discern what ideas are fit for attention, or what ideas are unfit for attention. This being so, he does not attend to ideas fit for attention, and attends instead to ideas unfit for attention... This is how he attends inappropriately: 'Was I in the past? Was I not in the past? What was I in the past? How was I in the past? Having been what, what was I in the past? Shall I be in the future? Shall I not be in the future? What shall I be in the future? How shall I be in the future? Having been what, what shall I be in the future?' Or else he is inwardly perplexed about the immediate present: 'Am I? Am I not? What am I? How am I? Where has this being come from? Where is it bound?'
"As he attends inappropriately in this way, one of six kinds of view arises in him: The view I have a self arises in him as true & established, or the view I have no self... or the view It is precisely by means of self that I perceive self... or the view It is precisely by means of self that I perceive not-self... or the view It is precisely by means of not-self that I perceive self arises in him as true & established, or else he has a view like this: This very self of mine — the knower that is sensitive here & there to the ripening of good & bad actions — is the self of mine that is constant, everlasting, eternal, not subject to change, and will endure as long as eternity.
This is called a thicket of views, a wilderness of views, a contortion of views, a writhing of views, a fetter of views. Bound by a fetter of views, the uninstructed run-of-the-mill person is not freed from birth, aging, & death, from sorrow, lamentation, pain, distress, & despair. He is not freed, I tell you, from suffering & stress.
"The well-instructed disciple of the noble ones... discerns what ideas are fit for attention, and what ideas are unfit for attention. This being so, he does not attend to ideas unfit for attention, and attends [instead] to ideas fit for attention... He attends appropriately, This is stress... This is the origination of stress... This is the cessation of stress... This is the way leading to the cessation of stress. As he attends appropriately in this way, three fetters are abandoned in him: identity-view, doubt, and grasping at precepts & practices."