Why are so many Twitter users badly behaved?

I looked up the words badly behaved in the Oxford English Dictionary and found this:

badly behaved, adj.

DRAFT ENTRY Sept. 2008  
Brit. /badli bhevd /, U.S. /bædli bhevd /, /bædli bihevd /  [< BADLY adv. + BEHAVED adj. Compare WELL-BEHAVED adj.]