If you are selling to get fiat to buy goods or services you also push a sell pressure to the coin or token and pushing the price down but if you use them as a payment you are increasing a value of that coin.
Not necessarily. How do I know that the person I am paying in bitcoin isn't also immediately selling it for fiat? All that has changed now is there is one extract transaction (from me to vendor) between the coin being sold for fiat. That's unlikely to have any impact whatsoever on the price. Many bitcoin payment services like BitPay are essentially just intermediaries which sell your bitcoin and pay the vendor the corresponding amount of fiat.
Try to find a way to buy goods or services with crypto instead of selling your asset and buy goods or services with fiat.
I also do this, and have convinced a couple of small merchants I regularly use to accept crypto, but sometimes it is just not possible. More or less everyone is forced to shop at some big chain or multinational at some point, and it's not possible for one person to get them to accept crypto like you could do with an independent retailer. If you are selling crypto to shop at these places, but then later replenishing your crypto holdings through earnings, trading, buying more, etc., then you are still contributing to the network.
I'd love to be able to pay for everything in bitcoin, but we are not there yet, and people spending bitcoin where they can, even via fiat, is still preferable to just holding it and never using it.