"A good portion of this skepticism is based on a myth – that advisers are a mob of unscrupulous salespeople who charge too much, and engage in obvious conflicts of interest by receiving commissions for pushing clients into expensive investments they don’t need."

The only part of that description that is mythical is the unscrupulous salespeople part.  I agree that the majority of sales people are decent and honest people with no intention of harming clients.

The majority of sales people are trained to sell proprietary investment product rather than to provide client specific advice - i.e. your typical sales person has a controlled inventory of investment product to sell with considerably higher fees than alternative but comparable investment options.  In many or even most cases the sales person really doesn't even understand the fee structure much less whether it is expensive.  Odds are the salesperson was convinced to buy the same product by the firm to perpetuate the "myth".