Something I've been thinking about for a while actually, but haven't been able to word up til now

I've seen a lot of 'you choose how you respond to comments' lately, not just on the forum but IRL as well strangely! I just wonder, where does that leave our own responsibility to 'speak to others as we would be spoken to'? To me, the former attitude cancels out the latter, KWIM?

So, where does our responsibility to watch our tongues end, and our responsibility to choose our reactions start?