Those who believe Buddhism is purely a philosophy point to the fact that the Buddha never claimed to be a god and even lectured against believing in divine intervention. Those same people also point out that the Buddha is "best know for" providing helpful techniques for dealing with real-world problems, and was a proponent of Vipassana, which adherents claim is non-religious and of benefit to people of all faiths - or people of no faith.
Unfortunately, their concept that Buddhism is only a philosophy is a product of their ignorance of the Buddha's life and teachings.
While many people view the Buddha's thoughts on being kind to all living creatures in a purely secular light, they fail to grasp WHY we should do this; the whole point is to escape the cycle of endless rebirths (known as Samsara) and to reach a final state of liberation (known as Nirvana).
Again, while there are many who believe that the Buddha's teaching in this regard can benefit humanity in the mundane world, the Buddha was concerned about the Supramundane. In short, the Buddha was concerned about what happens to us AFTER we die.
"He who seeking his own happiness punishes or kills beings who also long for happiness, will not find happiness after death."
He who seeking his own happiness does not punish or kill beings who also long for happiness, will find happiness after death.
Rouse yourself, be diligent, in Dhamma faring well. Who dwells in Dhamma’s happy in this birth and the next.
- Gautama Buddha
If there are benefits while we are still alive, then all the better. but they are secondary to to that which happens after death.
Those who doubt the religious aspects of Buddhism are quick to point out that the Buddha never proclaimed a theistic-based salvation; in short, the Buddha never said to worship or devote oneself to a deity for salvation (a practice known as bhakti). For example, the Buddha said:
By oneself the evil is done, by oneself one suffers; by oneself evil is left undone, by oneself one is purified. Purity and impurity belong to oneself, no one can purify another.
The Dhamapada, Verse 165
But these people confuse atheism with being are ligious. The Buddha is simply saying that our fate is in OUR hands, not the hands of a divine being.
However, there IS room in Buddhism for supernatural beings in the Buddhist cosmos; For instance, the Vedic deity Brahma appeals to the Buddha to teach The Dharma to lay people after the Buddha's enlightenment. But those supernatural beings are NOT above the laws of Karma and Samsara.
Many who deny the religious basis of Buddhism ignore the reasons that people originally followed the Buddha, and those reasons are based on metaphysical events. The ability of the Buddha to recall ALL of his past lives being one:
"A monk asked the Buddha, 'Under what conditions is it possible to come to the knowledge of the past and to understand the most supreme Way?' The Buddha answered, "Those who are pure in heart and single in purpose are able to understand the most supreme Way. It is like polishing a mirror, which becomes bright when the dust is removed. Remove your passions, and have no hankering, and the past will be revealed to you."
The Sayings of the Buddha in Forty-Two Sections
Kasyapa Matanga and Gobharana
These are just some of the basic concepts in Buddhism which point to the religious nature, and are common to all schools of Buddhism. This doesn't even take into account the Mahayana traditions which identify the Buddha with a supreme reality (known as Dharmakāya) which is identified as being eternal and moral.
And as for our friend the Marxist who believed the Dalai Lama's views on humanity are aligned with one of the most well known areligious thinkers, it might be a good idea to recognize that the only reason our friend even knows of the Dalai Lama is because Tenzin Gyatso is believed to be the reincarnation of the prior (13th) Dalai Lama. So you are citing the Dalai Lama, whose authority comes from the religious belief in reincarnation, to somehow validate your thoughts that Buddhism is NOT religion.
One other thing to keep in mind is there is no universally accepted of what a religion is. Some people define religion as requiring an anthropomorphic (human-like, or animal-like) creator (or creators). But not all people ascribe to that, and certainly it would be difficult to call those who worship sacred mountains, or oceans, or stars, of rain, as non-religious.
Likewise, many disagree about whether there are real differences between religion, faith, and belief systems. Further, it is difficult to determine if certain practices that are described as religious are really acts laid out by authorities or whether they might be local cultural practices.