Because they’re realised that the internet is full of trolls, idiots and spambots. And, seriously, who could blame them. It seems that science fact is something that can be debated with references to debunked or pseudo-scientific research (or even the Bible) in areas such as evolution and climate change.
Quite worryingly, they talk about recent research in which a fractious minority wields enough power to skew a reader’s perception of a story though the comments that follow it – and, with this, came to the decision to switch off the nut jobs:
If you carry out those results to their logical end–commenters shape public opinion; public opinion shapes public policy; public policy shapes how and whether and what research gets funded–you start to see why we feel compelled to hit the “off” switch.