Selling is bad, because when you sell BTC, you have less BTC and your ability to fuck the state diminishes.
It makes you more of a slave, it makes you weak and powerless.
Well okay, but if you hodl your bitcoins forever what impact does it have on you, on bitcoin, on economy in general? If money don't flow they are dead. If you want bitcoin to become stronger and be wider spread it should be used in different purposes all the time, the more often the better. It both gives sense to bitcoin and makes it more attractive to potential users.