I saw a thought-provoking post on Twitter about a week ago. It got something like 700 000 likes, and it's about one of my favorite topics: forcing people in a weaker position into doing the right thing.

The tweet's author has a younger sister. The sister is fourteen, and she wants to date a seventeen-year-old guy (the exact age difference is somewhere between three and a half years and four years). The author is polling the Internet to find out how many people think this kind of relationship is okay or not. She already knows the answer, I suspect; it's just that her and her mother's protests aren't working on her younger sister and she wants to use public opinion to reinforce the point. Of course, the overwhelming majority of people say that such a relationship will bring only pain to the younger girl, and, satisfied, the author walks away to presumably force her sister to stay away from that trainwreck.

She is asking the wrong question.

What she should be asking is this. Do I have the right to violate the trust and free will of my younger sister by using the economical, emotional, and legal power my family holds over her underage self if I have a good reason to do it?

I understand this is a private matter, but seeing as the author already opened the issue to public scrutiny by millions of people, she forfeited the right to privacy. So why not throw in my two cents? Of course, the information is incomplete, and I don't have much relevant experience, but this won't stop me.

Setup. The girl in question has been heatedly informed that such an age difference between partners is an eternity for a teenager, that the guy has much more experience than her, and that the relationship has every chance to turn emotionally or even physically abusive. She knows of the consequences but still wants to go through with it.

Option 1. Let her do what she wants and stand by for damage control. This will likely end in emotional damage, maybe in physical damage, very unlikely in pregnancy, almost impossibly in fatal STDs, and death in a couple decades. There is a lot that the family can do to prevent and mitigate the bad outcomes.
Option 2. Use emotional and financial blackmail, punishments, grounding, social media activity control, and all the other good stuff to force the girl into doing what the family wants.

I'm not as hot on the second option as everyone appears to be. Yes, it has a good chance of preventing a lot of pain. But the other side of the issue is that the girl came to her family for advice on this, she trusted them, and she gets put under guard and treated like a child. And no fourteen-year-old thinks themselves a child. Future trust on more serious issues gets damaged (at best), and if she decides to conceal the relationship from her family, the chance of her doing something very dumb skyrockets, because teenagers will rebel. Also, her elder sister uses a real name as a Twitter handle, so now the younger sister is exposed to the whole world as a child who can't decide who to date.

What I'm saying is that taking agency away from mentally capable informed people should be taken seriously as well as publicly declaring they don't have a right to said agency. Being told that your private life belongs to someone, because they have control over you and know better, is one of the most humiliating things that can happen to a person.