Is the universe just?

[anagogy]

Balancing and polarity has nothing to do with karma.

Your opinion, which you are entitled to hold.

If I just sit on my ass in the inner planes and do nothing, will the universe destroy my soul for not giving back the experience and light it gave to me?

It sounds like you are seriously misunderstanding the concept I'm presenting here. It sounds like you are thinking of it as a bunch of "i owe you's". It's not even remotely like that.

As I said, it is about as neutral as water seeking its level. Also, there are different kinds of karma. Water seeking its level could be viewed as a kind of "physical karma". It is just balancing.

Separation will eventually seek unity. So you wouldn't be able to sit on the inner planes forever. You would eventually be compelled to movement and change.

Why does forgiveness ameliorate a certain kind of karma?

Because it is a way of [drum roll] *balancing*.

The experiences that are attracted due to karma are imbalanced unity working itself back to balance. Forgiveness is letting go of imbalance.