I don't think anyone reasonable disputes that Best Buy has a right to do this. As a private company, they can do pretty much whatever they want provided it's not discriminatory against a protected class of people. However, if they do this, they must still obey the rules of contacts. This means, they have to be up front about this sort of thing. I think people are upset that they are having the rug swept out from under them when it comes to this stuff, and that is what's wrong.
The
return policy on Best Buy's website is pretty much silent on the issue of returns being refused or these letters they ask people to sign about being blacklisted. The closest they have is an explanation as to why you might be asked for an ID when returning something.
As far as I'm concerned, if I buy something and comply with all requirements written on the receipt, Best Buy is obliterated contractually to accept the return. So if I have the original receipt, and it's within the 15 day period (or whatever the period is), and I haven't damaged the item or otherwise done something which is expressly prohibited in writing beforehand, they can't refuse the return. No ifs ands or buts, no matter how stupid my reason for the return is. They can blacklist me afterwards from buying things going forward, but they cannot refuse the returns which I already purchased.
If Best Buy wants to be able to refuse returns because of customer doesn't like the color, or is upset that the battery was drained from the box, they should specify in their return policy what is and is not an acceptable return. Instead, they write "If you are not fully satisfied with your purchase, let us help you with a replacement, return or repair." They cannot then be upset when people take them up on it. They can't talk out of both sides of their mouth.