Any understanding that Newton's statement "for every action, there is an equal and opposite reaction" would mean balance is physically erroneous. When one extends "equal and opposite action/reaction" to a moral "if I do bad, I receive bad" (i.e. a retribution law, based on "Natural law" if not on God), there's still no balance…
Symmetries at one level can appear dissymmetrical at another: a car and a pedestrian will receive opposite forces on impact as per the Newtonian transfer of energy (which will link mass and speed prior to impact). At opposite speeds, the influence on one another might not appear symmetrical at all, though, due to their different deformation characteristics but also due to their different masses: the car will continue its course only slightly slower, while the pedestrian will brutally reverse course, but that's still a perfectly opposite action/reaction according to Newton… the car will not bounce back on impact with the pedestrian!
Perfectly symmetrical gravitational attraction may be too weak to prevent two objects (at least one with initial non-null speed in an appropriate direction) from drifting infinitely apart. But (depending on the speeds and masses), it might also be enough to crash the two objects in one another and 'fuse' them. That is to say the result of symmetrical forces in a system is not necessarily symmetrical: the system itself is not permanent, i.e. the initial system (2 bodies) will break down (to 2 bodies but without mutual influence, or 1 body… in any case, a different system).
Both results (infinite expansion, or collapse) would hardly be seen as a 'balance' similar to the solar system with bodies having speeds and masses that allow them to be on 'stable' orbits for a decently long time (assuming our solar system "forever stable" would only be an assumption).
Physics principles are not easy to master; meaningfully extending them to moral laws is even harder and there are many traps. Action and reaction are 'opposite;' does a good action lead to bad reaction? does a good action call for an 'opposite' good reaction? what is 'opposite' exactly?
The balance we're talking about is a concept, applied on other concepts… we create difficulties by projecting models (not reality, just models of it) from one field onto another. We assume the model is right (as in 'valid' and 'true'), we assume its permanence, we assume the possibility of extension… We basically don't deal with life, only with concepts we're clinging to in a quest for some sense of security and understanding what's going on…
Leading one's life on a 'reciprocity' principle (I do good, I receive good) is a form of spiritual materialism, and it leads to disenchantment the day you realise that loving only works without expectation of return; it also leads to disenchantment when looking at inequalities in the world (do you really believe people deserved dying of hunger, and some billionaire deserves to let that happen, because the former have done bad and the latter good?). On the spiritual path, one needs to drop the hope of a personal positive return.
One last remark: 'balance' or symmetry are not required for a sense of personal responsibility (as in "if I do bad, I'm the one to receive bad," because the reaction applies on the action / source, not on something else).
Personally, I take the lack of balance as the ultimate call for personal responsibility: if I want to perform or support wholesome acts, or change unwholesome ones, I have to take responsibility for that: no 'balance' will do the work instead of me, or for me. I cannot abdicate, or be patient; I'm the one in charge of how I use the energy I have.
(this post was inspired by a conversation triggered by George Kozi, cf http://plus.google.com/u/0/104341224517581649387/posts/EeFvvz2fVWv)
(on lack of balance calling for responsibility in shaping what we can, may I suggest reading the conclusion of 's http://plus.google.com/u/0/102162793011751589081/posts/56emYy6TN1V)