Practice that is dependent upon others is not genuine practice. By practice, here we mean primarily the hard work of Zen meditation, or zazen. That is, if one's practice depends upon the presence of others for support in the social or psychological sense, and one is not able or inclined to sit in meditation alone, one's practice is not mature, not genuine.
Of course, we are dependent upon others, even when we sit alone. This is acknowledged in the meal chant recited at most Zen centers, including the line: "We reflect on the 52 efforts that brought us this food, and consider how it comes to us." Especially today, we in the USA are overly dependent upon a long and complex network of people, organizations and machines that produce, package, and ship the food that appears on our table. The steps in that chain, and the efforts that bring us our food, surely surpass 52 by a considerable amount.
But, like Bodhidharma, we should be able to practice alone, in a cave. Even when we sit with a group, we are essentially practicing alone. An old Buddha said that you must do three fundamental stages in Zen yourself: renunciation, awakening, and clarification. He pointed out that that no one else can do them for you. This is why I say that Zen is the ultimate in DIY (do-it-yourself).