(like in case ETH, to create smart contracts).
Ok.. but create smartcontracts isn't the purpose of Ether (ETH).
Eth is the fuel of Ethereum network. It is used just as a currency to pay for processing power in the network.
It fuel transactions of tokens and dapps, which run smartcontracts. It is the currency used to pay the processing power of this "world computer". Its value comes from the high demand for that processing power.
But in case of latter, i.e. pegged money, there is no direct utility involved. Suppose I create two Ethereum tokens and name them WebbyCoin (WBC) and WebbyStabCoin (WBSC). I keep the supply equals to 10 million for both of them. Now I try paying you 5 million units of WebbyCoin for a freelancing work, would you accept it? No, right? Then I keep $10 million in my bank account, make the bank account public and tell everyone that these $10 millions represent the value of my WebbyStabCoin. IF you possess WBSC, you actually have share in this $10M. Now, you will gladly accept payment in WBSC. But it doesn't mean WBSC has any value, the value is just representation of $10M that I kept in bank account. If I withdraw money from bank, WBSC's value will instantly become zero.
I don't agree with any of that. If you say your newly created token is pegged to your bank account it will still be worthing zero, because no one trusts you. You can at any time withdrawal all your money from that bank account and pay no one.
Stable coins is simple put just a private debt. You decide to lend money to Bitfinex or Coinbase because you trust them. In return, you receive a token which they promise to pay back 1usd for each at any time.
Many people around the world trust them, this is why there are nearly 9 billion USD already borrowed to Bitfinex. It is valuable because of its high market cap, issuer credibility, and so on.
If you say you will pay back 1 usd for each WBSC, probably nobody will buy it for more than 0.01 usd. At least I wouldn't. Your coin would still be worhtless no matter how much you promise because you need to have a minimum credibility to ask for someone else's money.
Just my 2cc.
but if it's about a deflationary model like Bitcoin.
Bitcoin is not deflationary. At least not yet