When the law is wrong, it sometimes has to be disobeyed. Have you read "Civil
Disobedience" by the abolitionist "Henry David Thoreau"?
It is not desirable to cultivate a respect for the law, so much as for the
right. The only obligation which I have a right to assume is to do at any
time what I think right.
As for your financing system: if the user of a program needs to pay to modify
it, then this program is proprietary software.
As for the quality of free software: that is a secondary argument. One that
will not bring users to 100% free software because many of them would tell
you Photoshop is better than GIMP, MS Office is better than LibreOffice, etc.
Even if, at some point in time, free software is technically better than
proprietary software, that may change later and the users, who were convinced
by that argument, would go back to proprietary software. People must be made
aware of the essential freedoms they deserve as computer users. That is the
only way I know to never lose those freedoms once got.