The benefits are calculable, but the consequences of abuse are unpredictable, and if someone has crossed your boundary once, you don't know how far they will go.

With the abusive relationship example, if someone's gone as far as snoop through your phone and text your friends without your knowledge, there is no telling what they'll do next. It's common for someone who does this to also be a verbal and physical abuser, which is rarely worth sticking it out for, regardless of how well-connected they are.

With the specific LinkedIn example, they may e.g. sell your data to third parties, leak your data publicly via irresponsible data storage, and allow employees to access your data without authorization. Not to mention spamming your entire contact list with LinkedIn invitations in your name.

Is that worth it to you in exchange for some networking?

But right there is where the power of your metaphor breaks down. It is quite unusual for a website to also be a verbal and physical abuser (recent eBay cyberstalking being the incredibly rare exception).

I think the idea of a metaphor is that it is not literal, do you not agree?