There are various factors that might influence demand and supply, mere buying and selling won't affect it.
I disagree with the last words of your sentence. "Mere buying and selling" would lead to more supply and more demand at the same time - in other words: to more liquidity.
Imagine you are fearing a crash and prices at the exchanges are beginning to descend. If you panic now and sell your coins at an exchange, you will find yourself "deepening" the crash because you take out a buy order and chances are high the price falls further down. If you, instead, buy something for the BTC, then there are three things that can happen: 1) the merchant sells the coins because he's panicking too, 2) he holds, 3) he spends them.
Case 3 (spending), in a "Bitcoin ecosystem" where you can buy almost everything for BTC would be always an attractive option, and it would not have a "deepening" effect on the crash at all - it would only make Bitcoin circulate.
The more attractive case 3 is, the stronger the stabilizing effect.
You are maybe right that the nature of BItcoin's distribution/reward policy (with fixed
total supply) may have also a strong influence, but supply and demand theories still apply, at least explaining parts of the price movements.
What I meant was, people will stop using the refund back policies, there'd someother marketing strategy by then, and whatever happens, the community would go back to hodling again. Like you said, people were spending more in 2014-15, but when prices started to rise, they started hodling it. If ever, merchants, the more popular ones start accepting crypto, then the price will rise, at the same time, people will start stocking it, and sell later, and before you realize it, bitcoin becomes an investment again.
OK, I understand your point now about "increasing prices after more acceptance". Yes, there is always a danger that such a "revert to hodling" could happen.
But if merchants offer davis196's "refund policy", then it becomes attractive to spend the BTC even in bull markets. You can ensure you won't be hit by a sudden crash, but you also will profit if the price goes further up - and then you get some Bitcoins back
and the things you bought. And merchants would profit from high selling volume, too - so they will continue to offer these refunds, until the market turns to bearish again.
I can imagine this "scheme" to become a real alternative to hodling. And this would have also a secondary effect: As it's always possible that merchants sell the BTC at some time for fiat (e.g. to take out part of the risk) then there would be also more sell orders on fiat/crypto exchanges, mitigating the "FOMO" and increasing liquid supply. Above all I can imagine this to happen in the final stages of the bull market, when it becomes clear that a "mania" is taking place and sudden crashes are to be expected. A merchant with sustainable price policies would then probably sell as fast as possible, even suspending the refund policy until the mania has ended.
There's not all said, and maybe there are other effects, but overall I'm sure that usage would stabilize the price evolution - but because of the effects you mentioned, bubbles couldn't fully be prevented.