>In my experience most regular people first react with "Oh they wouldn't do that", and then after experiencing commercial software for a decade or so eventually realize they all eventually do that.
>From there, one can open a discussion to the solution which is open source.
As long as you keep them away from the apocalyptic discussions about systemd, or pulseaudio, or gnome3 vs gnome 2, or snapd or any of the many other "project has gone in a direction that some people feel very strongly about" kerfluffles that have littered the open source world and lead to many a fork. Or for something bigger than a kerfluffle, you could look at basically anything going on with RedHat / CentOS / Fedora in the past few years. Yes, in theory what happens here is that group B forks from group A and people who preferred A are happy and people who preferred B are also happy. In reality, users suddenly find themselves in the middle of deciding which camp they want to be a part of (especially if the split was over some item they don't care about, like systemd). And if they're really lucky, they'll pick a side that gets continued, ongoing development. If they're not, they pick a side that either gets abandoned by the forkers after their fury cools and the realities of managing the fork set it, or worse they wind up as a small-also-ran, slowly but surely deviating more and more from the "mainline" from which they forked and losing out on all the ancillary benefits that come from being the community de-facto standard/target.
That isn't to say that open source can't have a better degree of protection than proprietary software does. Just that open source by itself is no guarantee, and you might find yourself having to switch software and learn whole new systems just as much as you would if you were using closed source software.
For the absolute vast majority of users who are not developers, open source doesn't mean anything to them because they don't have the knowledge, or the money to deal with the open source software they use making the same arbitrary decisions any other software package might make. Yes, you could take all the source from the last release of CentOS and hire a bunch of developers to keep it going for you... you could also in theory buy all the shares of Microsoft and force them to make windows the way you want it too. The fact that the former is more in the realm of possibility than the latter doesn't make either of them a good plan.
Heck even for developers - if vim decided to start shipping everything you wrote to sketchy AI servers, if Ubuntu decided that all windows will only have maximize buttons and be unclosable without a restart, or if VLC decided to inject ads infront of every locally played video - I may not have the knowledge or skill set to find that and rip it out. Or maybe I just don't have the time because my bills don't get paid by correcting open source projects doing things I find stupid. I can hope other people will do that, but again, now I'm at the mercy of hoping the team of dissatisfied people maintain a fork forever, just like any other uses.