That sounds to me like a manifest of "I should say whatever I like, and no one has the right to say anything about it"
If you say so

You can tell me you're offended just fine, but you shouldn't expect the world to fold to your every wish, just because you are offended. Whether I respect your reason/claim or not is entirely up to me, just like its up to you whether you respect my reasoning to do so. We are all free, and nobody is holding anyone elses chains here except those who let the past chain them in the present.
I agree that intent is important. I was speaking to the continued use of those words after it's been brought to your attention that it's offensive. That changes the context significantly. If you know that using a particular word can be offensive and choose to still use it, then your intent is less valid because you now have knowledge of the word's reception.
Here's an example: I once wrote X-Mas instead of Christmas on a volunteer sign up sheet for a program that I was running. I was told by several of the volunteers, who were Christian, that they found that offensive because I was "taking Christ out of Christmas". Well, that wasn't my intent and, as an atheist, had no idea that it would be received that way. I was only trying to fit it on the top line and was using it as a shorthand. To me, it wasn't offensive. However, you can be absolutely sure that I never used that shorthand again. Why? Because I knew that, regardless of my original intent, people were offended by it. Had I chosen to use that shorthand again, I feel I would have been choosing to offend people.
Like you said, it comes down to choice. If in that situation you wanted to be accepted to them, well then you made your choice to change. Its a courtesy you choose to do, and there's nothing wrong about that. At the same time, if you didn't feel like writing the card over again because some people wanted their religious views to be pressed upon you, well didn't they not value your views in the matter at all? And what happens, now that you write christmas from now on, when someone else decides that christmas is an offensive term because it implies a religious meaning to the holiday that has become mostly secular? And the final question, is it really worth you going through the trouble of apologizing and changing and all the stuff just over a card? Why is it a card is suddenly so important in those peoples lives that they have to get all up in arms about it?
My philosophy is to do what it is you want to do, be it to be offensive because its not worth your time changing, or to be courteous and change for their preferences. Because otherwise you're just doing what everyone else does and defining all your choices based on what other people want, and not you. Maybe you'd like to write X-mas and save yourself the time of writing out the full name sometime? Maybe not?
But people don't have the right to make someone change something they're doing when the impact it has on them is so minimal and removed.