Martin Amis has accused Jeremy Corbyn of lacking a sense of humour. The jury is out on that one. Either way, a good joke is more than just a political skill, it is also humanity’s last line of defence.
http://www.theguardian.com/books/2015/oct/30/martin-amis-jeremy-corbyn-humour-jonathan-coe
Will you help me with understanding the bold passage from the above sentence? I am not able to find out the meaningful interpretation.