Nothing about it suggests it balances anything, and nothing good is supposed to come of doing good. The end benefit is enlightenment. Outside randomness isn't anything more or less special than human acts.
To try to put it briefly, by practicing compassion you attempt to lessen suffering. All karmic lines can be ended by compassion towards suffering. You cannot just go out into the world and end others' karmic lines, but you can end them when they pass to you.
If a dog bites a mailman (randomness), and this pisses off the mailman and he shreds important mail for the homeowner, who then becomes angered and slaps his kid for a minor offense, and that kid comes to your classroom and disrupts the class because he was slapped by his father, you now have the choice to find compassion for the child to help lessen suffering by the very least of not acting it out and passing it on, and even perhaps by not making things worse for the child, who could then enrage his father and mother all over again and on and on... you can see it spiral out. Your own attachment to things can cause this suffering. If your ego is bruised you will likely act in a shitty manner to someone else and they then have the choice to get pissed and be shitty, or to end that karmic line in themself and not pass it on.
If you do not incorporate the practice of compassion to end suffering, then you're not actually talking about karma, you're discussing some other concept of a positive energy bank.
And yes, I think karma can be perceived secularly, but not with the end point being some kind of nirvana, though I could argue a person who can end suffering is enlightened.