I really like GR and recommend it to everyone who is interested in their family history.
It's great for sharing info.
Yes, there are occasions where details have simply been copied from me ~ sometimes incorrectly ~ but this can happen anywhere. The same thing has happened to me on other sites and via other means. It can be very annoying at times.
I don't mind people using the information that I have researched, or which has been researched by others and passed on to me ~ but I do wish that they would acknowledge the people who really discovered it, & not just claim it all for themselves
I allow most people who want it to have access to my tree. I'm not sure that this is a good idea, because it means that they have access to information that isn't 'theirs' but which they can, and sometimes do, add to their own tree, anyway. (There may be stolen identity issues, too)
I rarely add living people to my tree ~ and never without their permission. But I take this further, and rarely add the deceased parents of living people, either. Usually this just doesn't feel right.
But yes, some people will just add everyone they find on someone else's tree.
I like to prove relationships first, too.