All excellent points.
There are ways (in real life as well as on a forum) of putting across a point of view in a discussion without being goady or confrontational.

For example, one can say, " However, I believe that..." rather than this or that 'is definitely the case and you're totally wrong'.

And to show one is listening and learning, one can say, "That's most interesting..." before giving an opposite idea.

Things like 'Have you considered?', 'That might be so but...'
'I respect your view, however I see it rather differently...' are much more polite than
'At it again (name)? More of your usual rubbish? You're an idiot/racist/anti-semitic/etc

The saddest thing is Iains' last point: 'The thread closes and good people run away.'