Honestly, I disagree that anybody can pass with a photo, because there are people who can't even pass then. Also, you can usually tell when people are trying to pass with only certain photos and the people who do "camera tricks" likely can't pass in real life (by most standards) anyway. I only point this out, because I've noticed that my opinions of who passes and who doesn't on here seems to be a lot more stringent in approach than most. At the same time, I realize that people who totally pass within the view of the camera lens may not even come close to passing in real life. There's a lot more aspects of a person's demeanor that factor into "passability".
As far as FFS goes, I think like any other part of transitioning, the person should decide they want it based off of whether or not they think it would make them happier with themselves - not what other people necessarily think of them. It's a personal decision, whether most people agree with them or not; additionally, trying to veer someone away from a part of transitioning is dangerous territory, especially if it's someone you care about. Even though it's likely intended as a compliment to tell someone they are "passable" enough already, that person likely doesn't agree and attempting to tell them that a step of transitioning they might want to undergo is "unnecessary" may only induce more self-hate in that person.
Bascially, they want FFS because they feel that it is best for them, and it isn't really fair to question that especially within the means of beauty and its ideals.