I was most surprised when clicking on a 'hot match' a while ago to be faced with myself!
It turned out that the lady who had put me on her tree is related, she had made contact with a cousin who I had given permission to use mine a couple of years ago, he had given her permission to use his... see where I'm going?
My first thought was indeed annoyance, then it occurred to me that I don't ask his permission to share my tree with anyone else so I am as liberal with his related section as he is with mine really, basically anything transferred to mine I assume ownership of and vice-versa.
I should add that I only keep about 100 names on my GR tree, just the direct lines where contact is most welcome and should a contact prove fruitful, they then get all the relevant info by e-mail and I ask them to be discreet with the living if applicable. If I get info back by e-mail which will be of interest to another relative, then I ask permission of the sender before sharing it.
I agree it would be courteous to ask first but in a place as public as GR I just don't think it's practical. If you had shared information with even half a dozen contacts over a period of time, it could be onerous to contact them each time you wanted to open your tree to someone else.
Sorry if I'm waffling, I do agree with you, but it's the nature of the GR beast, you have to share all or nothing. Although, if you specifically stated that you did not want your details published anywhere else, you might have some leverage if they ignored you.
Steph.