Great work, would love to try this out but I'm not going to link my Facebook to a random app.
The risk here is that I don't want the app creator to know my name. It's that simple—I don't know them, I don't trust them, I trust them less now that they ask for completely unnecessary information. Let's say traffic to this site is linked with lower credit scores: it's naturally absurd that the two are causally related, but it's a reality that I have zero control over how my traffic data relates to how companies use it. All I can do is reduce my traffic data from getting into their hands where I can help it.
The app saves you the gifs you like/disliked that requires a session. Now you could say the app doesn't have to save that information, but then I'd say it's a toy app so it doesn't have to do anything. The creator wanted it to save your history, therefore it requires a session.
Let's say it requires a regular email login instead of facebook (in order to support password reset). If you're using an anonymous email that you've been careful never to accidentally associate with your name, then yeah you could keep the app creator from knowing your name.
If like most people you just use your regular email address, it's trivial to get your name with a quick google search.
>Let's say traffic to this site is linked with lower credit scores
If you're really worried about that, then you should probably have an entire fake virtual identity to handle things like this.
I don't believe facebook allows this. Hence the problem with a facebook-only login.
Stop being a dick.
It's far more of a dick to force your users to reveal their identity.
EDIT: to be clear, OP is not a dick, but there should be a non-session or non-sso signin option (as there is now) if I want to preserve anonymity for what is essentially a (polished) toy.
Also the app didn't request access to your friends list.
That's beside the point though. You're worried that a random person on the internet has access to publicly available information that the entire internet already has access to.
The only extra information you're giving out to the owner of the site by logging in with facebook is that you are a user of this site. The worse thing the owner can do is publish that fact.
That is the only foreseeable risk. I can't imagine enough people are concerned with that risk to make it worth most developer's time to address.