If you can’t argue against your own beliefs convincingly then you really don’t have strong beliefs to begin with.
To me it seems only reasonable that if you wish to be an effective advocate then you must also seek to be an effective devil’s advocate, juror and jurist, commentator and debator all existing simulteneously with the other.
People that argue their position because they have ‘principles’ often ignore any data which does not support their position.
The claim of taking a position according to some principle is rarely based upon anything more substantial than ‘I already have an opinion and I am saving my brain capacity to decide what to have for lunch’.
If you really have principles and follow them, and believe them right for imposing upon others, then surely you have given thought to counterarguments and counterevidence. Surely. Surely … at least occasionally. Some evidence would be nice.