Naishkarmya no doubt is the ultimate spiritual state.  But, to take to total inactivity in its name is neither proper nor beneficial for a sadhaka.  Krishna makes this truth very clear by explaining the laws of Nature underlying material existence.

Whenever Krishna presents a proposition, he puts forward ample reasoning to support it. In fact, it is this abundant reasoning or rationality that distinguishes Vedantic thoughts from the rest.  Scriptures occupy a paramount place in our land.  Equally so is reason. Even to understand the true import of scriptural statements, reasoning and rationality are indispensable.  Thus you will find Bhagavad gita as much a rational presentation as it is an inspired outflow.

Sri Krishna disapproves Arjuna’s sudden fascination for naishkarmya:

None ever remains inactive even for a second. All indeed are compelled to be active by dint of the forces of Nature.

Prakrti – the aggregate complex Nature comprising the elements earth, water, fire, air and space, together with all their evolutes – is in a state of incessant vibration and flux. Days and nights, the different seasons, innumerable cycles - big and small - manifest as a result. The basic characteristic qualities (guna) of Nature are satva, rajas and tamas. Satva represents and manifests as taintlessness, brilliance, knowledge and happiness. Rajas results in activity, desire and attachment. Tamas causes ignorance, delusion, laziness and sleep. These three gunas, constituting the whole Nature, are inexorable and have their reign over sentient and insentient creation.

Everything existing in Nature is subject to the play and effects of these three gunas. Being so, Krishna says, nothing in the world can remain inactive even for a moment. Earth and planets revolve constantly; sun radiates without any break; within each atom there is incessant activity of the elementary particles. Is there anything absolutely inactive then ? Man’s body, organs and mind are also meant to be active. The food will be digested only when the alimentary system is active. The nourishment will be distributed only when the blood is circulating. The mind thrives only when the thought process is ceaselessly on.