Ok, so a lot of people are saying that they use those words all the time with their friends. I think the operative word here is "friend". Your friends know you personally so they are not offended when you call them that, because they know you respect them. I personally sometimes affectionately punch some of my friends in the shoulder, and they don't mind, because they know I'm not really trying to hurt them.
The difference here is that I don't go punching strangers in the shoulder, because they don't know me and have no reason to assume I am friendly.
You see, racial slurs and other insults that are specifically directed against a certain group are very charged. People in those groups have often been subject to those insults several times in their lives, mostly with the intent to exclude and dehumanize them, therefore they associate those words with hostility. When they hear someone use those words they assume that it is being used in a hostile fashion. Yes, you may not have meant it as hostile, but people are not mind-readers and therefore cannot automatically know that.
Using these words in public forums is particularly troublesome precisely because it is public. Anyone, from any group, may enter it and be confronted with words that are particularly traumatic to them, so it is simple courtesy to refrain from using such words unless necessary.
You are free to use them, of course, since it is your right. However, it would be rather hypocritical of you to dictate whether or not they're offended. They have just as much right to their offense, and often for good reason.
tl;dr: Some people are offended by slurs for good reason. It is common courtesy to avoid saying those words.
