I'm just going to say this, because it needs to be said- no matter who says it, this is total bunk. Taoist religion can't be a corrupted version of Taoist philosophy, because Taoist religious practices existed for thousands of years before Lao Tzu wrote the “Tao Te Ching.” Practicing Chinese Taoists attribute the origins of their tradition to the Yellow Emperor, not Lao Tzu. Saying something comes from the Yellow Emperor is a Chinese way of saying “it's so old no one even knows when it started.” Scholars of religion usually describe Taoism as a development from very ancient forms of Asian shamanism.
Is there such a thing as “Taoist philosophy”? Yes, the writings of Lao Tzu and Chuang Tzu can be described with this term, but the Taoist philosophical tradition derives from the Taoist religious tradition- not the other way around.
Think of it this way. St. Thomas Aquinas is a pillar of the Western philosophical tradition, but his philosophy is grounded in his Catholic religious faith. You can't separate Thomist philosophy from Catholic religion, because Catholic religious doctrine is the starting point for Thomist philosophy. Can you imagine anyone describing himself as a “philosophical Catholic” but not a “religious Catholic,” or claiming that Catholicism was a corrupted version of the Thomist philosophy? Of course not, that would be ridiculous- but people do the same thing all the time with Taoism.
So, how did this happen? During the era of colonialism, some Western intellectuals became fascinated with the profound philosophy of Lao Tzu and Chuang Tzu, but they couldn't reconcile the sublime ideas of these philosophers with what they perceived as the vulgar superstition of Taoist religion. So they engaged in a desperate act of wishful thinking, convincing themselves that the religion must be a debased popular version of the philosophy they so admired.
In other words, the whole distinction between philosophical and religious Taoism is inherently patronizing, derives from the false assumptions and projections of colonialism, and has no validity at all.