[brebory]

They sum up their reasoning pretty succinctly here: https://yourkarma.com/help/75-why-do-i-have-to-login-with-fa...

[Groxx]

Because it's so hard to make a fake Facebook account. If someone actually wants to cause trouble, requiring Facebook won't do anything except slow them down for about 20 seconds. I see this "reason" everywhere, but it's total garbage.

[artursapek]

Seriously. That's asinine.

[plink]

"Vomitous" is the word that came to my mind.