[ccppurcell]

This is a false dichotomy between spending the first third of your message on niceties and being maximally blunt. I don't agree that you do not owe other people a modicum of consideration about their emotional state.

I advocate a middle ground and also empathy and curiosity. I think you can keep in mind that you might be wrong and treat people with respect without wasting their time. Something like "please check these lines/this function/whatever again. I think it will have such and such an effect. I did this test, here's the output". Seems fine to me.