Dating apps do this too; one of the major selling points of Tinder's premium plan is that you can see who swiped right on you.

They're not at as much of a risk though, as it's much more difficult to begin a chat with a Tinder user than it is on Linked In. Knowing the profile ID or whatever won't help you, if you can't open their profile in-app and swipe right on it, you can't begin a conversation.