I don't sell (much) at the tops. I don't want to be known as the guy who bilked lots of suckers out of $ if Bitcoin fails. I want to be known as a guy who identified BTC's potential as a force for positive social change through economics early and invested accordingly.
I don't see how selling at the tops is immoral. If anything it is praiseworthy, since selling at the top and buying at the bottom will smoothen out BTC's price, resulting in lower volatility and greater usability for commerce, store-of-value etc. .
Selling at the top gives you the ammo needed to buy at the bottom.
By buying at the bottom you are showing your faith in the continued existence of bitcoin, and stop a feedback loop of declining prices leading to less interest and a smaller network.