I think it is not wrong in selling the coin but the problem is when you choose to sell bitcoin, because time will determine the price and determine your profits
If person needs money whatever the price, whether high price or low, it's not wrong to sold their bitcoins and convert it to fiat.
Why it's wrong in the first if obviously you really need it? You can earned it again anyway.
What you said is correct, if everyone just hold the bitcoins and no one will sell then how will the price will increase or decrease, until their is no trading and price fluctuations we cannot see more development in bitcoins. Their are so many country where you cannot buy anything in bitcoins so they convert in fiat currency and meet their expenses.
I am also doing the same as i am earning bitcoins weekly and this is like a salary for me doing the bitcoin job, i keep 20% as investment balance i convert some and some i do sports betting .
Yes without dump there will be no pump. Most of the traders are not enthusiast to buy coins at highest rate so in most of the cases they will do something to make it drop. Then that will be a cycle of pump and dump resulting for price increase and decrease.
And some people like bitcoin price to become accepted in most of the shops. If that will happen, expect a quite stable price in bitcoin.