Selling coin to yourself can preserve profits, if it's keeping the price up. Paying the fee to the exchange is trivial
Whenever I sell coin to myself to preserve profits I do it OTC, in person. That way there are no fees at all and no counterparty risk.
Just kidding. How does selling coin to yourself "keep the price up"? Isn't that crazy talk?
Well, let's see, I create 2 accounts on any of a number of bitcoin exchanges, I put in a sell order at a high price using one account, and then I buy the exact amount of coin at the high price with the other account (No one sane will buy my coins at the high price, so I can even let the sell order sit for a few days). Now do this 10,000 times per day with bots (exchanges have APIs), and you get a price graph that looks similar to the current exchange rates... Was that hard?
Since I'm doing 10k transactions per day with an exchange, they love me and charge lower fees, or even give me kickbacks. Market sites like coinmarketcap report a huge transaction volume, and everybody assumes that lots of commerce is happening, which perhaps leads to more investment in the space?