you must not sell. but i also disagree with you for other reasons.
purple might not be the most potent, but it does carry a very specific taste that i do like every once in a while. some strains can also be pretty damn potent (usually never as potent as the same strains green pheno counterpart though), you must not have had a lot of different kinds of purple, or just got unlucky.
i think the beauty in a purple plant is something that cant be overlooked as well, but i love to garden also- i dont just have this hobby so i can smoke, i thoroughly enjoy the process.
lastly as a seed collector i think its important to keep the genetics around, and i like to maintain a huge variety in my stock
peace