An Advaitin does not defend against any argument as He needs no defence :He is not different from the argument also :)
But Lord Krishna comes forward to defend Him with His Gita :
4.22 Remaining satisfied with what comes unasked for, having transcended the dualities, being free from spite, and poised under success and failure, he is not bound even by performing actions.
4.23 Of the liberated person who has got rid of attachment, whose mind is fixed in Knowledge, actions undertaken for a sacrifice does not produce fruits for him.
5.7 Endowed with union with Brahman [yoga-yukta] while being devoted to the performance of the nitya and naimittika duties. pure in mind, controlled in body, a conqueror of the organs, the Self of the selves of all beings-he does not become tainted even while performing actions. [The construction of the sentence is this: When this person resorts to nitya and naimittika rites and duties as a means to the achievement of fully Illumination, and thus becomes fully enlightened, then, even when he acts through the apparent functions of the mind, organs, etc., he does not become afflected.]
5.8-5.9 Remaining absorbed in the Self, the knower of Reality would think, 'I certainly do not do anything', even while seeing, hearing, touching, smelling, eating, moving, sleeping, breathing, speaking, releasing, holding, opening and closing the eyes-remembering that the organs function in relation to the objects of the organs.
5.25 The seers whose sins have been attenuated, who are freed from doubt, whose organs are under control, who are engaged in doing good to all beings, having attained absorption in Brahman.
A real Advaitin therefore does not stop his activities. He becomes engaged in doing good to all beings and so teaches others the path of liberation, while enjoying the bliss of being one with everything internally.This state is really beyond any argument. Sri Krishna refers to this state by the words 'pashyato muneh'.
The 'Vedanta-Sara' also points to the same inaction in all actions after the jivanmukta comes out of the Nirvikalpa Samadhi.(219-221).
In 'Viveka-Chudamoni' also we get:
The gentle-natured great saints live by doing good to all like the sweet breeze of Spring. They being liberated want to liberate the suffering ones surrendering to them. Thus is their greatness.(37)
A real Dvaita-vadi on the otherhand will never come forward to teach anyone as He will be indrwan in love of God and would not spare a moment without looking at or serving his beloved.He will be mad in love, as Narada points out in His Bhakti-Sutras.The Braja-Gopikas never taught anyone or preached any doctrine.