Secular Buddhism is for many an oxymoron.  Here, the incomparable teacher Thinley Norbu Rinpoche shares some words on the subject.

"There have also been lectures available on the Internet about "the secular Buddha." This kind of negative characterization cannot be given for the origin of all positive qualities. Buddha is ceaseless, everywhere and in every time, unaffected by anything. Buddha means that all obscurations are purified, including the reality phenomena of human beings who think they are either secular or nonsecular, and that all immeasurable wisdom has expanded. Although Buddha can appear in any aspect, Buddha cannot be put in the tiniest category of secularism.Buddha is fully enlightened with wisdom body, wisdom speech, wisdom mind, wisdom qualities, and wisdom activities, which are indivisibly pervasive and inconceivable, and at the same time manifest in an immeasurable way, so one cannot say that Buddha is either secular or nonsecular. It is ridiculous to try to expel Buddha from Buddhism, which was named after Buddha, and make even Buddha into a nonspiritual conception that can fit into the materialism of ordinary society with its different theories, groups, cultures, laws, and everything that belongs to the worldly phenomena of samsaric beings.

A secular Buddha does not exist, since secularism belongs to society and ordinary beings and is not even connected with religion. More than religion, Buddha is wisdom, beyond belief or disbelief, neither aligned nor unaligned with anything, with the power to emanate as anything. So, Buddha cannot be put within one small nonreligious category. Secularism is not a term for fully enlightened Buddhas who are beyond all conception, including conceptions of society and religion or the rejection of religion.

Buddhas are beyond all samsara and enlightenment, and also at the same time emanate toward all samsaric beings, not only secular beings, and pervade throughout all of the enlightened state, so they are forever stainless and beyond all thought. Buddha cannot be made to belong to this world, other worlds, or even this universe. Buddha is nowhere because Buddha is forever like stainless sky.

One cannot catch or make stainless sky, but at the same time it pervades everywhere. Just like stainless sky, Buddha is everywhere because Buddha manifests effortlessly and unobstructedly within any realm, place, and time. It is absurd to try to limit this manifestation, like trying to hold all of the immeasurable sky in one small pot. Even if people cannot practice formally or traditionally, they still need to believe in a simple way, and no one should be trying to stop this."

[Spacing added for online readability]