The phrase that appears in The Book of the Law is "Do what thou wilt shall be the whole of the law", not "all of the law". And from the very beginning he explained that there's a distinction between doing "what thou wilt" and "what you want". In The Message of the Master Therion he writes:

[I]t should be clear that “Do what thou wilt” does not mean “Do what you like.” It is the apotheosis of Freedom; but it is also the strictest possible bond.

For Thelemites, one's will is a dynamic purpose in life, that's what they strive to fulfil. This is at the very basis of the religion, and nobody interprets the phrase as base sense gratification.

And you call the book a precursor to LaVeyan Satanism. That's a claim that's often repeated. Crowley influenced the entire modern occult movement, he didn't influence LaVeyan Satanism more than any other current. Calling it a precursor implies that Crowley was a Satanist. He used that symbolism, but he didn't worship Satan, therefore he wasn't a Satanist. Feel free to post a link that proves otherwise if you have it.