there is no crime in selling your bitcoin either to buy back or to use it in solving your needs. is it not your investment? why should you not sell it when there is a need to? if after buying your coin you continue holding without selling, of what purpose is it to you? if i one can only buy bitcoin and can not sell it when he dims it fit to, then there is no point in buying it at all.
Is not like we should hold bitcoin for a lifetime but the idea of selling your bitcoins will depend on the stage you are in your investment, someone who is still accumulating bitcoin don't need to think about selling yet except if the person have reached his accumulation level where he feels that he doesn't need to accumulate more again and that is when a sizable portfolio have been achieved and even when you plan to sell at that time, you don't need to sell all, you can take some profits from it while still holding. And if there is nothing tangible you need money for; it will be better to leave your bitcoins untouched and allow it to experience more growth when the price skyrockets