OpenSource is preferable whenever possible, but as in anything else, fanaticism is harmful when a good proprietary soft offers a better solution
I think an engineering perspective is useful: we want to solve problems, but different people have different problems, and each person cares about each of their problems to a different extent. If one person thinks their problem is that a relevant amount of their income depends on proprietary software, then the solution is substituting free software to replace proprietary software they depend upon. If another person doesn’t depend on proprietary software for their income, but thinks it’s a problem that their thermostat runs proprietary software, then the solution is still to substitute free software to replace proprietary software (or to replace the thermostat entirely). However, if someone wants to increase their income tenfold and using proprietary software will accomplish that (and using free software will not), then the solution is to use proprietary software.
It’s probably better to help people learn and understand how to use free software than to encourage them to use proprietary software, since free software is probably easier to maintain as someone’s situation changes, but there might be some situations where the best solution for someone involves using proprietary software.
Technical problems and political problems can be related, and discussing one in the context of the other can be useful.