Now it's your time to get reactively emotional.

I never said an emotional response dismisses the merit of the argument. ;)

In the blockchain space, you can't get all of the three at once: decentralization, security and scalability.

To this i have to say that i find all those things about Bitcoin debatable at best. For security youre arguing basically from the point of size and ill argue that there are other ways to provide asset security to a reasonable degree that you wouldnt have to fear losing your $$$ that doesnt require blockchain at all. Decentralization i find to be overvalued (and debatable) and not nearly enough of a reason to adopt it.. Scalability i wont really argue with bitcoin, lol.

All of those things are provided better by other cryptos.
The question is:

What does Bitcoin do for crypto that no other crypto can?

My answer is: "Absolutely nothing".
If the question was:

What has it done in the past?

Then i would say "A lot".
But we dont live in the past.

Bitcoin and gold are the hardest forms of money humanity has ever had.

I dont agree with that statement at all. I dont see Bitcoin or Gold as money. Neither of them fulfill enough functions of money. Bitcoin less so then gold.

Steem's value proposition is enabling freedom of speech. The high and unstable inflation of STEEM makes it impossible for STEEM to become a widely used currency.

Yeah, i dont agree with that either. On free speech, sure, but STEEM has exactly the same base fundamentals as any cryptocurrency. Cross border payments, its basically free to use, no fees, 2 second transfers. All those attributes make it better then any crypto that claims to not be a utility token and wants to compete with Bitcoin.
Bitcoins deflationary nature makes it impossible to be any kind of basis on which you can build a world economy.
While Steem might be a utility token and im happy with it remaining as such, the inflationary aspect (although unstable atm) would be a much better basis for being adopted as money over Bitcoin.
It would need a drastic shift in perception and use case and while it is highly unlikely to happen, the potential is at least there while i dont see Bitcoin having any kind of potential to achieve that same thing.

Fiat currencies are propped up by the fact that governments have tools of coercion at their disposal to make using them the path of least resistance and the fact that central banks have hoarded a full third of all existing physical gold.

Government coercion indeed is where the value of fiat comes from. But no one can argue that there is no value in that. You have to create something that provides value beyond that level and i dont see Bitcoin achieving that at all. Remember, the populace were willing to give up all their rights to dictatorships and communist governance. We havent changed that much in 30 years.

Again... Gold.... As much as the space seem to love it, i dont see gold, outside its industrial application as something that is inherently more valuable then fiat thats backed by globally entangled government coercion. Its use case trumps anything Gold can provide in terms of being money.

If Bitcoin grows sufficiently and if fiat currencies continue to be debased at an accelerating rate, central banks may begin to purchase Bitcoin to gain possession of currency with a hard cap.

Youre saying here that if people buy more bitcoin then people will buy more bitcoin. But you can make the same argument for any crypto out there.
Bitcoin lives on its brand, first mover advantage and im saying that project like steem at the same MC would provide magnitudes more value to the whole ecosystem. Its not even close. Its like a Olympic jumper making the leap of 10 meters and another one leaping to Mars.

Im not saying Bitcoin wont go to 100k. I never mentioned price once. Im saying that Bitcoin at 100k would still be a pestilence on the crypto space once it moves to 50k after that. Im saying that there are at least a hundred projects out there that could achieve much more right now with higher Market caps. Steem being one of them and the speculation tied into bitcoin will potentially ruin all of them.

Thats why i call it pestilence. :D