Diplomatic approach is the modern way of stating, "you need to learn how to lie to people's faces better."
I would disagree.
A diplomatic approach is getting someone to understand your perspective, you understanding theirs, and coming to some sort of mutual arrangement or agreement. This is why accomplished, skilled diplomats are almost never caught in a lie when they're actually at the table (rather than PR and other publicity statements). Lying is counterproductive.
It's intentionally avoiding inflammatory statements while retaining the meaning. Saying that 'I disagree' comes off as much more diplomatic and much less hurtful than 'you're wrong' even though they can sometimes mean the same thing.