I think the ticket is that Fe is social glue, though best when authentic as well, definitely, it's used to smoothen things over and keep the peace, especially in groups. Fi is what it is, the only thing it's really got going for it is that it's genuine and authentic. It also somewhat feels like the connection you have between lovers, in that it inspires trust, and loyalty, vulnerability, and opening up to one another, at least, ime. Those things are incredible, but they have to happen in an environment that is completely safe. To disarm someone like that while being careless with their fragile state is...negligent at best. To manipulate with Fi feels like an oxymoron, though it is possible to enhance your own genuine enthusiasm to create a desired effect. To use that effect to gain something from someone and potentially harm them in the process is a breach of trust that's often irreversible, not to mention cruel, and ultimately the exact opposite of what Fi is supposed to do.