When confronted with such "advanced" questions as karmic retribution, I always return to the four noble truths. Buddhism is grounded in an end to suffering. If karmic retribution were fundamental to Buddhism, then one would have to suffer to be amply punished for ones past "sins." A little suffering? Lots of suffering? Disabled? Sexually abused? What is the point of retribution if we learn to accept our pain but let go of suffering? None are innocent; all are innocent. What does it matter? No one is a victim. It is all karma.
I was sexually abused as a child and use a wheelchair today. Never have I thought of my abuse or disability as karmic retribution. My pain, regardless of its source, from karma in this life or past lives , is merely focuses my practice to end suffering.
I don't agree with the idea that "birth defects or "crippling" diseases" definately being the "consequences of bad karma from previous existences." Patrul Rinpoche (1808-1887) wrote in THE WORDS OF MY PERFECT TEACHER: "The best incentives (to enlightenment) are enemies, obstacles and the sufferings of illness." How could any karma be "bad" if the worst of times lead us to the best of times, i.e., enlightenment?
I do think that karma - that is mutual causality or dependent co-arising - from this life or past lives does preclude free will and is a form of "hard" determinism. The idea of "free will" is another illusion arising from the illusion of there being an "I" who decided and does. All actions of all things impinge upon us and we, with them, mutually cause all actions within us and . It is true that our acts have consequences, but I don't know about "natural laws" if such laws are considered external, like gravity. "Acts against others" damage us because there is no them or us, no external or internal. It's all one system.
Of course, the question about karmic retribution implies that we have had past lives. Since the Buddha said it "does not lead to profit" to discuss lives other than this, I will remain silent as well. :-)