If people dislike tattoos, that's not offensive. They just have a different opinion. If we all felt the same, the world would be boring.
If people make the assumption that people with tattoos are stupid/chavs/idiots, that is offensive. However, it's best to just write these people off as narrow-minded, and not pay any mind to what they are saying.
If people openly discriminate against people with tattoos - turning them down for jobs purely based on the fact that they are tattooed, shouting at someone in the street and calling them names because they have tattoos, etc - that's unacceptable, and they should be called out on it.
Unless people fall into the third category, which I haven't seen anyone doing on this thread, I can't get too riled up about it. I'll defend tattoos, and defend the people who get them, but I wouldn't get drawn into any kind of silly argument with them. If people fall into the second category, I tend to just write them off as knobs and leave them to their frothing.
Some people are too defensive about their tattoos, but it's understandable. To me, my tattoos are like a piece of precious jewellery, but with the extra importance of it being on my skin, permanently. They represent my family, the illness I overcame, the major moments in my life, and when someone calls everyone with tattoos uneducated, or chavvy, I do find myself getting defensive, because it feels like a criticism of what they represent.