Scarcity doesn’t exist because anyone can start their own blockchain and pretty much anyone who can has. There’s nothing preventing anyone from relaunching an exact duplicate of bitcoin with all of its strengths and weaknesses at any time other than inertia.

You are missing the point here. It's about the history of the individual coin not about the technical properties of coin in itself.

You can build as many cryptocurrencies as you want to. They aren't bitcoin as they don't have the history of bitcoin which means that they aren't the same.

Only bitcoin is bitcoin, because only bitcoins has the history they have.

Bitcoin forks like Bitcoin Cash and Bitcoin Gold use the same block chain history as Bitcoin.

You are also missing the point here. You can't get the same for bitcoin cash as you can for a bitcoin. So no they don't use or have the same history after the fork and they aren't the same which is why one is 4 times more worth than the other.

Of course you cant get the same for them! It is expected that a fork that creates new coins out of thin air will lead to cheaper coins.

And so scarcity still exists which was the original point I made and which was being challenged.

Each coin has a unique history. You can create as many forks of bitcoin as you want it doesn't change the fact that there is only one bitcoin.

right and anyone can start their own twitter too

I can go get a printer, and start printing stale2002 dollars, right now, perfectly legally.

Does that mean that paper money isn't scarce?

Dollar bills, of course, are protected from counterfeiting, in the same way that bitcoins are.

That would be legal, but critically attempting to redeem them for current USD would be a crime.

So no... not the same.

It is exactly the same.

First of all, I COULD sell my stale2002 dollars for real dollars, at market price, as long as I am not lying about what I am selling.

The price of my sale2002 dollars would probably be ~0, but I am still not breaking the law.

If you fork Bitcoin, you can't redeemed your forked coins for real Bitcoin, either.

It would be a completely new and different currency.

The same exact thing is the case with my new paper bills.

With the Bitcoin Cash fork I can spend my coins on both histories. That is the opposite of being scarce.

You can't sell Bitcoin Cash for the same price as you can sell Bitcoin. So no it's not the opposite it's exactly what I said.

Is anyone actually auditing all these blockchains?

You wouldn't have to that's the whole point of the blockchain that the validation is done by the network itself.

All you need is to know which coin/token you are on and you know whether you have the original or not.

I think what he/she meant was the code base

Yes and thats missing the point.

Perhaps. How do you know who controls the hashrate?

An integrity verification service for [the codebase of] ICOs and other coins would be a welcome innovation