This is a really bad idea. Most people don't change defaults -- the idea behind DNT is that the people who care about privacy can easily take steps to assure their own privacy. As long as businesses know that browsers sending the DNT header are sending it intentionally, there's a chance that websites will respect it.
With this change, DNT becomes meaningless. How can businesses determine which users are OK with being tracked, and which are not? Since it's technologically easier to simply track everyone, and it makes good business sense to gather as many metrics as possible, businesses will simply argue that they can't respect a header that most people don't know/care about (since it was on by default). That makes things worse for the people who do care about it.
First, everybody cares about privacy. Just because businesses have taken advantage of users being clueless, doesn't mean those clueless people don't care about privacy.
Second, your "nobody knows about it" argument can cut the other way. How can a business track people when most people don't know/care that they can opt out of being tracked?
Nobody wants to mention it, but the truth is that if it were on by default, few people would turn off DNT once they knew what it was for.
I don't like MS, and I don't even own a computer that can run IE10, but I think this is a great idea.
I spent several years working for a marketing firm and based on my experience with the industry I would guess that there will be no adoption of honoring these tags if they are sent by default unless it becomes legally mandated.
Well there's really nothing Microsoft can do about that, is there?
It seems silly for marketing firms to tell everybody, "Oh yeah, we're totally serious about privacy and we'll honor DNT," and then backtrack when lots of browsers start sending it.
Other than companies like Google most marketing companies couldn't give a shit about what you think of them as you aren't their customer. Additionally a lot of marketing companies would likely publicly get behind a DNT header when the recommendation is that browsers send "no preference set" by default. As soon as a browser vendor goes to default DNT the marketers support of the standard and honoring of it will go out the window as it's not in their interests to participate any longer.
The end result will be that Microsofts choice will result in everyone being tracked rather than only those people that have no preference set or have explicitly opted in.
A good example of companies not honoring a restrictive default is the P3P header. Damn near everyone sends a P3P header but most of them don't actually honor the settings from the header, or have the other components set up. It's all about getting third party cookies set successfully and not honoring how MS implemented P3P in IE or what the user wants.
If you say everybody cares about privacy you should back that up (unless you are using privacy in the general term and not for this specific example). I, for one, do not care about site tracking; in fact, I would gladly opt in to any such service if I see it fit. And I know a lot of people who also do not care about tracking.
Well, I guess we'll find out when people start complaining that the internet ads they see aren't as relevant as they used to be and Microsoft relents and turns DNT off.
Most people do not understand how all this works well enough to even know that they have something to complain about. They just want their Googles to work and show them interesting things. If the ads they see are less interesting, they aren't going to say, "Huh, I wonder if Microsoft started sending an HTTP header which falsely indicates that I prefer irrelevant ads." No, they'll just lump it in with all the other stuff that doesn't seem relevant to them and ignore it. Which of the parties involved in that situation wins? Not the browser implementor, not this particular user (who doesn't care), and not any of the advertisers who now have to waste money talking to people who are unlikely to be interested.
This is true, but it's also a very broad statement that does not entail that many people care about the Do Not Track header. Everybody has a different level of privacy that they care about. Most people care if you watch them in their bedrooms or bathrooms. Some people care if you know how much money they have. A smaller number of people care if you see their bare skin and thus wear burqas when they go out in public. An even smaller number of people care if ad networks compile a profile of things that are interesting to them.
The problem is that "Do Not Track" is supposed to indicate intent. If the browser vendor indicates intent in one direction when the user hasn't indicated intent in either direction, advertisers can no longer trust what the browser tells them. It's like the boy who cried wolf.
With this change, DNT becomes meaningless. How can businesses determine which users are OK with being tracked, and which are not? Since it's technologically easier to simply track everyone, and it makes good business sense to gather as many metrics as possible, businesses will simply argue that they can't respect a header that most people don't know/care about (since it was on by default). That makes things worse for the people who do care about it.