"well, if you care about that person, you can explain how proprietary
software harms her"
This seems like a perfectly reasonably thing to do, right? Even a caring
thing to do. But as with pointing to consumers of liquor and tobacco that the
substance they are dependent on is harming them and is best avoided, people
who are dependent on proprietary software will often get angry when someone
points out that it is harming them and is best avoided. This is often the
case even when communicated in a respectful and non-pushy way. It's difficult
to be a conscientious person in a world where most people blindly follow the
herd at their own expense, and get incredibly defensive when examples of this
are pointed out to them in any way (even by other people's choices not to
follow the herd).
Calher, you are obviously a really conscientious person, and it sucks that
you feel that this makes your life more difficult. I encourage you to focus
on the many ways it also makes you life better.