Diplomacy is not merely a discussion between interested parties. Discussing cricketing heros or fine art may be useful in establishing common interests, but resolving conflict is done with diplomacy - to convince other parties that changing their stated position is better than having the negotiation fail.

Passivists who claim 'war is never the answer - diplomacy is' do not understand human nature and self-interest.

It is pointless for a buyer to bargain for an item if the seller knows they are willing to pay the full price - the seller will simply hold out. Likewise diplomacy is useless without the threat of force or disengagement - the opposition will simply hold out.

Saying 'I would be really happy if you did X' is pointless when negotiating. It merely demonstrates your incompetence and lack of understanding. Diplomacy only works when there is a price to be paid if the negotiations fail - like refusing to trade, or going to war.