The story about the hard left president of the NUS- Aaron Porter- being racially abused by the ultra left student activists was not something I found surprising given the nature of the extreme left. It was all to believable to me.
Others though found it incredible and demanded further evidence that the event had actually happened. At first I assumed that the writer was making excuses for the protestors because he sympathised with their cause until I noticed that the arguments he gave for disbelieving the reports were very similar to the arguments made to refute claims by a black liberal congressman that he had been racially abused by a Tea Party protest. I found that refution very convincing.
There are some differences in the stories and the latter story was marginally less plausible- but even so that isn't the real reason why I believed one refution of racist abuse immediately and treated the other one as being weasel words trying to defend the indefensible. It was because I was guilty of a cognitive bias that encouraged me to judge the evidence depending largely on which conclusion I wanted to hear.
I'm not remotely unusual in that regard but it pays to remember it.