@RustyBertrand since we’re talking about courtesy, I don’t think it’s reasonable to take offence at simple disagreement. When it becomes discourteous is when it strays into personal insults or attacks and deliberate confrontation.
I think reasoned arguments is what most of us are here for - agreement is not a prerequisite, but some modicum of decency is and I think that constitutes courtesy.
“Do unto others as you would have them do unto you” is still a good yardstick.