Deriving preferences is not inherently bad. It's immoral to undermine people's will for profit. This is the same reason the gambling industry is immoral, and

Deriving preferences is not inherently bad. It's immoral to undermine people's will for profit. This is the same reason the gambling industry is immoral, and making manipulative free-to-play mobile games is immoral. You're basically hacking people's subconscious for your own gain at their loss.