This is a fair enough argument but some goods and services you can only pay for via fiat. In fact most goods/services can only be paid for by fiat or credit. Inflation is going to be a thing at all if you are just selling the amount of BTC you need to make a purchase in fiat. I am guessing you mean exchanging for large amounts of fiat that you wouldn't be using in a few days time.
If you will used bitcoin on buying thing it is much better if you will just hold and not sell it for more earning and for future development of the price and value of bitcoin. But in terms of trading selling of bitcoin is quite vital for you to earn and have profit because the basic principle of trading is to buy when it is low and sell when it is high. It is just a matter of decision making and your goals. Also make sure that you will always look selling as a form of trading so you could possibly earn.