Why do I make this point? Because I think we currently have instances of precisely this phenomenon.
I have in mind one or two commentators whose keenness to promote the cause of a particular party and to denigrate others leads them to demonstrate scant regard for differing views, or understanding of the constraints under which politicians have to operate, and to exhibit over-the-top and unpleasant attitudes - derision for those who disagree, a lack of compassion for those who look to government or society for help, a readiness to bad-mouth those of our fellow-citizens who are doing it tough.
Not only is the quality of our democracy damaged by the display of such attitudes, (since we should be able to handle our differences without impugning the competence or good faith of those with whom we disagree); but we all suffer if we can no longer trust what we are told and conclude accordingly that no one in public life can be trusted.
The Americans, saddled as they are with a Trump presidency, are in course of discovering just how damaging to a functioning democracy a constant diet of lies and loss of trust in the media can be.
In the New Zealand context, the irony is that it is not just our public life in general that will suffer; the fortunes of the party favoured by the commentator can also be adversely affected. Many readers and listeners will conclude that the distasteful views and opinions expressed do not just spring unbidden from the mind of the commentator, but faithfully reflect those of the party being supported; and, accordingly, an unfavourable reaction will inevitably rub off on the party which is the intended beneficiary of the "attack dog's" supposed help.
It may be that the party supposedly "favoured" in this way may have very little to do with what is essentially just a piece of "free enterprise" and self-promotion on the part of a self-appointed champion. The lesson is that political parties should take even more care in selecting their supposed friends than they do in identifying their enemies.
The media themselves are also in obvious danger of being tarred with the same brush as the commentators to whom they give a platform - a decision that they alone take and for which they must take responsibility. They, too, like the social media, need to recognise their duty to maintain the health of the public debate. If that debate is damaged, they - as well as their readers, viewers and listeners - will be the losers. And we are surely at a point when we should recognise how important it is to be kind to each other.
• Bryan Gould is a former British MP and Waikato University vice-chancellor.