One should not abandon his own natural pursuit even if it has a taint of evil. All activities are indeed enveloped with evil, like fire with smoke.
Krishna goes a step further to point out the true nature of all activities. He shows that ultimately viewed, no action is to be unduly preferred or abhorred. It is parochial to think of any differential approach, letting in the trap of discomfort and narrowness, as it happened with Arjuna in Kurukshetra.
He preferred to abandon war and be an ascetic. Krishna clarified matters for him. Remember: We are in the last lap of the dialogue that followed. Krishna raised Arjuna’s mind and reason from the so-called dvandvas like good and bad, virtue and vice, making him float in the ecstasy of oneness.
He says that all undertakings in the world are associated with one kind of evil or another. Therefore, do not discredit the task you are naturally given to by inheritance, compulsion or chance, and think of adopting another. To do so will be a grave mistake, a real sin, causing downfall! Avoid such pitfall by all means.