“At Twitter, a fight erupted on an internal message board after a worker who didn’t have children at home accused another employee, who was taking a leave to care for a child, of not pulling his weight.”

Well that’s pretty beyond the pale. What’s going on with your coworkers is not your business (other than whatever personal/professional relationship you're maintaining). If 1 worker taking leave is putting undo strain on you, that’s a business problem. Go tell your manager that he needs headcount and then go do your job.

This is a root-level issue that cyclically results from & continues the uneven benefits. When workers spend time slap-fighting with each other, it makes it even easier for management to means-test benefits like this