facebook sign in mobile number

Facebook Sign in Mobile Number

I just went to Agar.io to pass some time and just as I tried to log in via my Facebook account I was told I wasn't allowed to log in until I fixed some things on Facebook. So off I went to Facebook and I'm told they want my mobile phone number in order to continue using my account!!
So I click the question "Why do I need to verify my identity by providing my phone number?" and it says this:
We want to make sure that this is really you and that you’re connecting to Facebook with just one account.

To verify your identity, you'll need to log into Facebook and follow the on-site instructions to add your mobile number. Your phone number will be added to your profile, but you can choose who can see it there.

Note: Maintaining more than one account is a violation of the Facebook Terms.

What is this BS? My Facebook is a throw away account used to login to various websites so I can play their shit!! I don't give a shit about Facebook, never posted anything on there ever. I don't want to give my phone number. "We care about your privacy", "We care about security", bla bla bla. I don't want them to know who I am that's the whole point. There's even options to send scans of social security cards and drivers license! I'll pass thanks. Now I've lost all my progress at tons of websites.

How does it improve security anyway? They still don't know it's you, all it says is that you got hold of a phone and used it to link to that account. Even if they need it to verify it's you, someone can impersonate you if you get hold of their phone, that's even worse security.

It doesn't really "require" your mobile phone, for basic usage at least. They've been asking for mine for over a year now and I've been declining it.

And to be fair, if you don't want Facebook to know who you are, then you're using it for the reasons it's not intended for. They have been known to close accounts/force changes when you use a false name in the past. And yes, the initial setup is based on assuming that the person accessing the account is you. Past that though, unless they manage to steal your phone and get your account information, it's an increase in security, like if someone hacks your account and changes your password, you can use your phone to get access back.