You didn't finish your metaphor, let me.
I don't let anyone in my house, therefore what? Therefore I am joining a worldwide program whereby I am able to find out from a source I choose whether I want to let this person into my house. If they don't make their information available to my trusted source, they ain't getting in.
Also my house happens to contain things that billions of people want to see and use, but they have to sit through my time share pitch first. And they HAVE to listen.
> If it's being implemented it's because it solves a real problem.
If something solves a real problem, must it then be implemented?
Also, it solves a problem for web sites, and in such a way that non-malicious users will be less free to use the web the way they want.