You appear to have been out-foxed by someone with more far reaching subcommunity internet powers than yourself. He, obviously, knows how to play the internet sales and popularity game, and has far more power to do so than you.
To reflect on the question, why wouldn't Lawrence specifically want a forum, I'd suggest that its because he wouldn't be in charge. Per the comments in the reddit, he appears to enjoy a lot of influence in the places he chooses to frequent, making him defacto in charge of his own communities therein.
More generally, I suspect that a fan forum has little to no affect in any direction regarding sales. We often see people basically outright refusing to participate in more than one particular social media - ie, Facebookers stay on facebook, redditors stay on reddit, etc. The existence of a specific place likely only attracts people looking for that place, and does little to detract from any other.
The fear that it would drive down sales seems totally ludicrous. Popular things gain popularity by being popular
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