I think you're right here, but the qualifier "all things being equal" can't be taken lightly. Rarely if never are "all things equal." I also don't think a shift in the market context is necessary. We already have a market place where people who feel tricked or duped will have a lower opinion of the company doing the duping. dark patterns have a bad edge to them too--very few of them, when noticed by the user, leave the user actually feeling good about how they were duped.

This kinda reminds me of the talk PG gave at 2008 start up school titled "Be Good." (http://www.paulgraham.com/good.html or https://www.youtube.com/watch?v=q7K0vRUKXKc) He outlines many ways why it's not merely ethically appropriate to be good, but also a strategically superior approach to running a startup. Ease of use, simplicity, trustworthiness--these are important qualities of a biz's reputation, both internally and in public perception. And Dark patterns tend to harm that reputation.

Edit: Addendum--obviously there are monopolies or monopoly-like situations where reputation isn't important.