"Join nothing" means avoid group-think; avoid associations which will limit one's ability to think critically and independently; be your own man or woman; draw your identity from your own resources, and not from group membership.It does seem at first sight that remaining "unjoined" indeed helps the philosopher remain objective in his quest for the truth. But on the other hand we have the example of Socrates who, far from being unjoined, was perhaps the antithesis of the aloof philosopher. He was at one time a soldier in the Athenian army and was respected for his bravery in battle; even as he critically examined Athenian religion, he scrupulously followed its duties, down to making sure religious rituals would be followed on his demise (his last words were "we owe a cock to Asclepius", Asclepius being the god of medicine.) More deeply, he viewed his vocation not merely as a personal, independent search for truth, but in the context of his duty as an Athenian citizen:
For if you kill me you will not easily find another like me, who, if I may use such a ludicrous figure of speech, am a sort of gadfly, given to the state by the God; and the state is like a great and noble steed who is tardy in his motions owing to his very size, and requires to be stirred into life. I am that gadfly which God has given the state and all day long and in all places am always fastening upon you, arousing and persuading and reproaching you. And as you will not easily find another like me, I would advise you to spare me. I dare say that you may feel irritated at being suddenly awakened when you are caught napping; and you may think that if you were to strike me dead, as Anytus advises, which you easily might, then you would sleep on for the remainder of your lives, unless God in his care of you gives you another gadfly. And that I am given to you by God is proved by this: - that if I had been like other men, I should not have neglected all my own concerns, or patiently seen the neglect of them during all these years, and have been doing yours, coming to you individually, like a father or elder brother, exhorting you to regard virtue; this I say, would not be like human nature. And had I gained anything, or if my exhortations had been paid, there would have been some sense in that: but now, as you will perceive, not even the impudence of my accusers dares to say that I have ever exacted or sought pay of anyone; they have no witness of that. And I have a witness of the truth of what I say; my poverty is a sufficient witness. (The Apology)Socrates was not an autonomous philosopher pursuing a personal career, but a man on a mission fulfilling a duty given to him by God for Athens. For Socrates, then, the philosopher is by nature "joined"; this is the reason he refuses to flee Athens when given the chance to escape prison while awaiting his execution.
But does not his commitment to Athens make Socrates "biased"? I think it is a mistake to view Socrates's relationship to Athens as a "commitment", which is a word with an arbitrary flavor to it. Socrates was born and raised in Athens, and only left it when serving in the Army. He was raised by Athenian parents, educated in the Athenian fashion, and is Athenian through and through. His identity is Athenian whether he wishes it to be or not; he is "joined" to Athens not so much in that he has made an arbitrary decision to reside in Athens, but that his being is Athenian to its core. Were he to attempt to adopt a perspective that was somehow independent of Athens, he would merely be kidding himself, for such a perspective is mythical - and Socrates knew it. Man is by nature a creature embedded in culture; culture isn't like a coat he can discard for a new one (or, worse, no coat at all), but is part and parcel of his identity.
The philosophical quest, then, is one that must be conducted in and through culture. Rather than attempting an impossible abstraction from culture in an attempt to avoid bias, the philosopher is better advised to plunge more deeply into culture. The example here is St. Thomas Aquinas, who generated the supreme synthesis of medieval philosophy by embracing to the full his cultural identity as a Catholic and as an inheritor of Greek rationalism.
But suppose Thomas had been born a Muslim rather than a Catholic? Then he may have become an Averroes or Avicenna, Muslim philosophers whom he engages in his Summa. He may have perhaps even come to the point of converting to Catholicism. But the only subjectively true (in Kierkegaard's words) way to do this would have been by embracing his Muslim faith and critiquing it from within, as Socrates critiqued Athens from within. This is why philosophers of divergent faiths like Avicenna and Aquinas could respect each other, for their respective embrace of their cultures served as an indirect communication of their shared subjective understanding. The philosopher who attempts to remain aloof is not a part of this unspoken community; the attempt itself shows that he is confused at a much deeper level than that of objective doctrine.
This also shows us the answer to the perennial conundrum: If you had been born in Iran, you would be a Muslim, and if you had been born in India, a Hindu. You were born in New York of Catholic parents, so how can you claim that Catholicism is the one true religion? It is quite true that if I had been born in India, I would have likely been a Hindu, and it would have been right and proper to embrace that religion through my education. But I hope I would have taken a Socratic attitude with respect to it, and discovered the truth on the far side of a "joined" critique of it.