I'm going to try to pop the balloon of cryptocurrencies like Ethereum and Ripple

I'm going to try to pop the balloon of cryptocurrencies with the following scenario for Ethereum which is a smart contract blockchain platform highly touted as functionally useful and superior to bitcoin for business purposes and therefore deserving of a high coin value. I'm going to question how can Ethereum justify any particular valuation when it does not matter what the valuation is for a smart contract to be executed. My conclusion will deduce that the only reason Ethereum (or any other functional coin) has any particular value is merely because of speculation of perceived value, not any real value. Here goes.... So as an example, if someone was buying a home with a smart contract platform like Ethereum, they would have to purchase enough ETH coins equal to the price they are paying the seller and the seller would have to agree to receive those ETH coins as payment provided all contract terms are met. But upon fulfilling terms of contract and transaction of ETH coins, the seller would likely sell those coins into USD because the volatility of the ETH value is not predictable. Thus those coins are only transiently used on the platform. Neither party desires to own ETH long term.

That would be the case for most transactions. Wagers, purchases, etc. Buy the coins when you need to enter a contract, but exit when contract is fulfilled. You don't have to buy a bunch of ETH coins and hold them for some future TRANSIENT transaction. We are not doing a transaction for the purpose of collecting and keeping the coins like, er, coin collecting.

Matter of fact, the contract can stipulate only begin the conversion of USD to ETH the instant the terms on contract are fulfilled, and also instantly convert them from ETH back to USD when seller receives them. Then it does not matter what the value of ETH coin is at time of transaction.

Even IOTA has no mining and no transaction fees. So what does it matter what the price of IOTA coin is?

Matter of fact, most coins are like monopoly money. I can arbitrarily say Monopoly $1000 bill can be exchanged for $1 USD for smart contract purposes. I guarantee that the conversion will be accurate and instant. The seller can convert the monopoly dollars back to USD upon receipt instantly as well at same exchange rate. In this process we will document the transaction with blockchain. A week later, the exchange rate may be Monopoly $10 bill equals $1 USD. Doesn't matter. Another transaction can occur with same secure results. The value of Monopoly bill does not matter and is not driven by the transaction needs. So if the price of the ETH is not driven by any particular transaction, the coin does not represent any share of the company (as stock shares do), and it does not matter what the price of the coin is to perform a smart contract transaction, then there is nothing that support the value of Ethereum other than pure speculation and greater fool theory.

Same can be applied to the recently red hot Ripple (XRP). Financial institutions are lining up to use the platform for speed, able to scale, low cost, etc to move money from one institution to another. But again, when they need to make the money transfer they will convert to XRP for use of the blockchain platform, and upon receipt convert back to fiat currency from which it started. The use of the XRP as a mode of transfer is TRANSIENT. It does not matter what the value of XRP is at the time of conversion and re-conversion. Institutions do not need to horde XRP for some future transaction needs. It is a use-when-needed platform. Get-in and get-out of XRP transfer execution. There is no value in XRP. The value is in the blockchain record keeping at lower cost than centralized method.

Some exceptions. Some platforms are structured to systematically increase the value of the coins themselves. They have some built in method that gives real value to holding coins. Some method of systematically reducing the number of available coins and paying a dividend to coin holders based on profits accumulated by the platform are a couple examples of ways to give some value to holding coins.