Other social media sites have been doing it. Do we want to join in?
EDIT: Some people are saying that this is a power that ought to be left to communities… do we have a specific delineation of powers that relegates these decisions to communities? If not, then I recommend that these users propose such a delineation of powers. I would be very ok with this proposal failing because instead we got a more explicit set of checks and balances.
Personally I would go so far as to ban links to any social media site that requires a login to even view the content linked.
But yes, banning Twitter links has plenty of other good reasons for it too.
I think that that is a good general rule that is flexible for future instances.