Then might there be broader considerations that motivate you to defend the hypothetical numbers of Arnold's theory? As an artist yourself, you're not somehow invested in his claims of van Gogh's acute intermittent porphyria, are you? Well, I hope not. That is I wish you good health and a strong constitution.
But Dr. Arnold certainly is invested in this theory of his. As an outsider, when I read a 2006 article about him that states:
needless to say I'm quite impressed by the respect he's garned on the subject. Seems he's been able to build quite a career out of it. I would guess his theory constitutes an important cog in the world of van Gogh studies. There's probably a whole school of thought in art historical circles that base interpretations (and reputations) on his theory. As an outsider to all of it, I'd be inclined to believe that he has a vested interest in maintaining data that supports his position, however weak, inadequate or false subsequent research may show it to be. And not just him.
During the last 18 years, he has visited many places where the 19th century artist lived and worked. Arnold has lectured on van Gogh in Europe, Australia and almost every state of the U.S. In 1993, he spoke at the Dutch Reformed Church in Zundert, Netherlands, van Gogh’s birthplace, and he contributed the lead essay in the catalog of a blockbuster van Gogh art exhibition in Melbourne (1993) and Brisbane (1994).
Of course, I could hypothesize other reasons for your interest in supporting exaggerated thujone claims, but seems the least complicated reason for now.