It may seem appealing to the average user to be encouraged to use the same account information everywhere (contrast with what every tech will tell you, which is the opposite), but it’s just not proper.

This may be a bad analogy, but it feels like if your employer were to say, hey we don’t use our own keys, so let us just modify your own housekey to fit our doors, we promise it will be safe and it will still work in your house. That may be true, but my house key is a very personal item. I don’t care how safe the procedure is, this is my key, you have no right to use it, and you shouldn’t need to ask in the first place.

These places want your traffic, but not bad enough to support their own user system, something everyone else has done themselves since user/password systems were invented. I still feel like I’m not quite putting my finger on the issue, but there it is.

This is all of course, in addition to the security, privacy, and potential lockout concerns.