> your hardware is probably supported these daysTrue. Support has gotten significantly better. It's not perfect, and the failure cases are much worse than Windows (and somewhat worse than OS X), but it's gotten better.
> you should not buy hardware that is incompatible with the operating system you plan to use
This is where you start going off the rails.
People did buy hardware that was compatible with the operating system they do use. It is super presumptuous and weird to try this sleight-of-hand in your argument.
> LibreOffice supports the formats and works great
You are now off the rails and airborne.
Nontrivial Excel spreadsheets break in LibreOffice Calc on the regular and it's significantly slower (!) than Excel besides; anything using VBA, which is still a pretty big chunk of serious Office users especially in enterprises, is a nonstarter for obvious reasons. The UI is also, IMO, a huge step backwards from Office and now that the Ribbon "but but it's different" is far enough in the past that pretty much everybody has switched, another UI switch is probably not worth it.
> with Steam and Wine combined your potential gaming library is HUGE
Sailing through the air with the mountain approaching.
Your potential gaming library is huge--and either indie (which is fine, but limited) or largely broken. Suggesting WINE to somebody who doesn't already know what they're in for is dirty; even gold-flagged games in WINE that aren't a decade old are often broken in ways your average mortal can't fix. If you enjoy being elbow-deep in a computer, this may be fine for you. Most people aren't. Your preaching ignores this. It shouldn't.
> Proprietary operating systems work against your interests. Stop using them.
You've hit the cliffside. There are no survivors.
People will stop using them when open-source ones are good at the things they want. Right now, they're still not, and exhorting people to use an inferior good (for the things they care about) is kinda just doing people dirty.
Don't get me wrong: I would like Linux and other open-source operating systems to be better desktop OSes for normal people (and some of my own projects are intended to help facilitate that) but still, in 2017, it is a raw effing deal for the majority of people to switch to it. This should change. I know you work on stuff to make that happen, and that's awesome. But it's still not something I think can be recommended in good conscience to most folks, even around here.
It barely works for me, and I've been using it on the desktop for fifteen years and have grown accustomed to the need to cultivate tragically low expectations around the whole stack.