> The real question is: where do we draw the line between protecting people from manipulative design and respecting their ability to make their own choices?

Spoiler: There is no line. Societies (or more accurately, communities) attempt to self-regulate behaviors that have perceived net-negative effects. These perceptions change over time. There is no optimal set of standards. Historically, this has no consideration for intelligence or biology or physics (close-enough-rituals tended to replace impractical mandates).