The rationale behind copyleft licensing

In order for the world to be a good place, we must do good things.
We mustn't exploit the resources of the world willingly.

Now, some people are willing to do that in spite of others not doing the same.
And being a good person involves doing the right thing regardless of what others do.
That also means helping others even when they harm you.

But this is the part that's problematic.
Good people share the techniques they develop for everyone's benefit.

We expect them to be good people.
But they will never be.
That is why we have laws.