I am not sure if I can explain that. It's difficult enough to explain feelings in one's native tongue, but in a foreign language..
What I mean is: it's ok if they draw it on their body where others don't see it (unless they especially desire it). However, most of the times tatoos are plain ugly and you'd really prefer not to see them. Yet if they are displayed in plain sight you can't avoid seeing them - you are practically being forced to do something you dislike. The feeling of being forced against your will makes you aggressive and angry and you'll dislike the tatoos even more.
Oh dear - I really express myself quite poorly. My point is that I would prefer to have a choice. I don't want to have no alternative to looking at bad tatoos. People who don't cover their tatoos violate other people's rights to not be offended esthetically.
Plus, people covered in really bad tatoos always remind me of old school tables, daubed with scribbles, doodles etc.