The issue here is a failure of the upper-brass at BBY to understand even rudimentary economic & marketing principles. Let's assume Best Buy is not spouting hogwash and that the company actually does break-even or lose money on selling the iPhone X outright. Fine. Why is that a bad thing?
It's called loss-leading. You willingly accept a loss on a flagship item to get customers in the door, then you bombard them with relevant products and marketing strategies to entice them to purchase other items that have a higher profit margin. Even if you only convert about 20% of those sales (which is extremely low, and realistically should be much higher), at the very least you have reinforced an existing (or sometimes new) customer relationship and collected relevant customer data that could be monetized into future sales revenue.
Instead, Best Buy showed that they either A) don't have any basic-level understanding of sales and economics, B) don't have faith in their lineup of complementary products or their sales team's ability to convert upsell opportunities, or C) they are so out of touch with the consumer that they fail to recognize the negative publicity and impression that will befall them due to this practice. It's called the "zero f**ks" mentality, in that they literally have zero f**ks to give about their consumer or what they think.
I mean, it won't stop ME from shopping there because I'm too rooted in their system: rewards, VISA, etc., and also because I am determined to always get my price-match (yes, I have price-matched an item for $0.01 price difference, just on principle alone), although I won't ever buy an iPhone there, that's for sure. But, I know, especially in larger metropolitan areas where competition abounds, it will drive at least a few customers away from their doors on a long-term to permanent basis.