All executable images delivered to users should be accompanied by buildable source code corresponding to the image, if at all the image can be upgraded.
Moreover, it should be lawful for licensed users of a program to share source code modifications with each other.
This is not a copyright issue at all; the rule would apply equally to freeware as well as to programs which are not freely redistributable.
The whole problem is that software can be machine translated from an easily understandable and modifiable from to a cryptic form that is vastly more difficult to understand and modify. This source-to-image translation paradigm gives rise to abuses and problems which were not imagined by the people who invented copyright.
For instance, if you and I both buy copies of the same novel written in the English language, all of its sentences are plainly understandable. You and I can discuss, say, alternative endings for the novel, and even write them up in our mutual correspondence. We could do the analogous thing with software: all that stops us is that we received it in a gobbledygook compiled form. (Plus some idiotic EULA clauses about "reverse engineering").