It seems to me that satisfying customers is a better business plan than snubbing the competition. I expect some B&N customers may become alienated by B&N's policy and depart for Amazon just out of spite.
I wonder whatever happened to positive values. It seems like too often now that people want to go negative, perhaps because they perceive negativity has more benefits than positivity, perhaps a reflection on the world's present negative zeitgeist.
Oh well, I don't buy from B&N anyway. I always buy from Amazon, and just save up my book wants until I've got $25 for free shipping. That's even easier than figuring out where the nearest brick and mortar bookstore is. And cheaper. Amazon has seriously good prices (but mostly when you shop around).
More often than not I buy my books used on Amazon, usually picking sellers with good rep and books with "like new" descriptions, with about a 97% success rate. The very few that didn't satisfy were either easy to return for a full refund or got a reduced charge.
I mostly buy just cookbooks and a few "how to" hobby (art) books. I get all my fiction at the public library. I don't want to buy books I'll read only once. I prefer to buy reference books, like cookbooks, books that I'll refer to time and time again. Julia lives on!