As well as being a bedrock principle of the law, it's also basic common sense. If I accidentally step on your toe, that's obviously different to me deliberately stamping on your toe in an intentional attempt to injure you. If you set out to deliberately injure your colleagues then this is OBVIOUSLY different from doing the same thing accidentally and should be treated differently - and anyone with a working brain can see this.
The idea that "intent doesn't matter" is preposterous. Accepting it as a premise leads to insane and preposterous conclusions that no-one believes. People who say that "intent doesn't matter" don't actually believe it.
If intent matters (as you say, anyone with half a brain knows it does), then if you receive my comment as being offensive, I am still right because I didn't mean to offend you. What they want is to make sure they can tell me I'm wrong anyway because the person was offended... hence, my intention didn't matter.
Obviously it isn't a binary situation with either intent or impact being the sole arbiter - so the baseline used in almost all situations is the 'ordinary' or 'objective' standards. These can vary depending on the environment and context, and are simply defined because they are hard to define across all scenarios.
I guess I find it surprising that a code of conduct like this should sway between intent and impact in quite so binary a fashion -- human behaviour isn't software.