Because words mean things, and some words carry hatred in the very fiber of what they are. If you can't respect the fact that words carry very specific connotations, then you shouldn't be using them to begin with.
Furthermore, the "I'm at home, you're at home, don't be offended" argument is just plain ignorant because you know very well that you specifically choose your words to put down or insult other people. You are deliberately using the language you choose to elicit a very specific reaction, and any claims otherwise and this claim that people shouldn't be offended by your offensive language is just absolutely stupid.
Instead of telling people not to be offended, how about you stop being nasty to people and pick your words more carefully?