Leaders from a number of retail startups—Casper, ipsy, Shippo, and others—participated in an open discussion about their businesses at a Tuesday breakfast roundtable at Fortune’s Brainstorm Tech conference in Aspen, Colo. Amazon (amzn, +1.43%), whose stock price soared above $1,000 per share for the first time this year, remained the inescapable center of gravity.

Julie Bornstein, chief operating officer at Stitch Fix, a clothing subscription service, said that people suffer when a single company monopolizes a market. “It’s a danger to consumers to let Amazon use AWS [Amazon Web Services, the company’s cloud business] to price everyone out of the business,” she said. (Amazon’s margins for web hosting far exceed retail, a position that allows the company to subsidize its e-commerce business.)

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Laura Behrens Wu, CEO of Shippo, a startup that makes logistics software, agreed and identified what she considered a weakness in Amazon’s approach. “What Amazon’s not doing well is using Instagram, Facebook, and Twitter to create…