I'm not talking about the necessity of a certain belief. I'm talking about the meaningfulness and purpose of living the path of ascetic renunciation. If the view of continued birth and death in saṃsāra is denied then the monastic path as prescribed in the vinaya and suttas becomes an unreasonable and entirely unnecessary way to live one's life. A far more reasonable choice would be to live a life engaged in moderate pleasures.
As someone who does not believe in rebirth, I concur. This was the conclusion I reached myself after trying to reconcile the Dhamma with rational skepticism.
Certainly it can be beneficial to practice non-attachment and renunciation to some degree
if we have only one life; it will keep us from addictive and harmful behaviors and allow us to live well in the present. But the Dhamma, as I understand it, goes much farther than that. It is a path leading to complete eradication and cessation -- a null state, if you will, totally detached from the world of emotions and senses.
In a one life scenario, this seems like a curious aim to pursue -- since we will get there sooner or later anyway, at the moment of death! Meanwhile, we would be better off enjoying a life of moderate pleasures, finding a meaningful vocation, pursuing scientific and intellectual inquiry, contributing to the betterment of society, and/or cultivating loving relationships.
The goal of any life practice, it seems to me, has to be grounded in some logic. Cessation as a goal follows logically from a belief in rebirth and the lower realms. It does not follow from the belief that each of us has one life that terminates at death. What follows from the latter is something like the following:
Meditation is understood to be a means of “being here and now,” “of coming to our senses,” of acquiring a fresh sense of wonder. We practice the Dharma to better understand our own minds, to find greater happiness and peace in the moment, to tap our creativity, to be more efficient in work, more loving in our relationships, more compassionate in our dealings with others. We practice not to leave this world behind but to participate in the world more joyfully, with greater spontaneity. We stand back from life in order to plunge into life, to dance with the ever-shifting flow of events. (Bhikkhu Bodhi, The Challenge of The Future: How will the Sangha Fare in North American Buddhism)
The above actually represents my own perspective. But I would agree with Ñāṇa and others that this is not the Dhamma as taught in the Pali Canon.