Why is doorstep harrasment still legal?

Ever heard the phrase an Englishman's home is his castle.  I used to think that was a really grown-up (ie boring) thing to say.  Now I have a home of my own I can see what it means. I - the co-homeowner - decide who comes in, I don't even have to open the door if I don't want to.  My friend - the wise girl I was discussing this subject with intends to put a notice on her door that basically says, 'if we don't know you we won't be opening the door'  Which throws up all kinds of problems - all those packages you have to sign for that won't get delivered, publishers clearing house cheques, the passer-by who has just spotted your garage is on fire....    My parents have an airlock between them and the front door so they can open the door shake their heads and close it again without a word being exchanged.  Unless its the JH's and then Mum hides under the table until they've gone - I am not making this up!

I tend to take direction well, a sign saying 'NO TRESPASSING' will stop me in my tracks.  So will a sign (like the one on our front door) that tells you to read it before you ring the doorbell.  People who ignore that sign and aren't people we know or a appointment that we have set up, or parcel/pizza delivery are likely to get an earful from hubby (if he's home) or me.  But ignore it they do and then they wonder why  I'm so short with them.  It could be because I was buried inside my washing machine trying to extract the filter, balanced half way up a ladder, had just got my head around a concept and the doorbell sent my thoughts flying to the four corners or the fact that the doorbell scares the hell out of my cat. And when I do open the door they launch straight into their sales pitch.  The words "I'm sorry to bother you," would go a long way in this situation.

If I am in the front garden however, I'm fair game.

Update : Privacy film on the window at the front door, you can see them and they can't see you. People still ring the doorbell they just don't get an answer unless we know them. Simple but effective.