You don't need to remove choice to push better UX and software. It's not a zero-sum game here; we can foster better conversations with people in the Linux community and start talking about what would make the experience better for the average user, not just technically proficient power-users.
> Everybody using the same software creates a monoculture which is more prone to attack than a diverse ecosystem.
That's wrong - you're using a sort of strawman argument. What makes Windows a monoculture? There's a much larger, thriving developer community on that platform with many more developers making free and/or open-source software.
> You're going to have a harder time of that if you target Linux.
"Achkshully..." Linux has had some serious bugs, but the damage was relatively low to end users because of it's low adoption rates. It has very little to do with "Linux is more secure because we're diverse" and everything to do with "1% of end users use Linux, so the target is less likely to be worth my time." And furthermore, that 1% - the majority will be more technically proficient and less likely to be tricked into running arbitrary software.
> one normie's Windows machine
This. Is. The. Problem. Framing an end-user as a mentally deficient 'normie'. Why? What's the point and what's to be gained from this?
> And who are we to tell someone what they should do with their volunteer time?
No one is suggesting we tell hobbyists / volunteers what to do with their time. What people are suggesting is that we spend a little time talking about tackling common problems together, rather than re-inventing the wheel every single time.