Everybody has a right to free speech or expression; however they should also be mindful of others.
Now I have no idea what she was wearing on the day of the flight (indeed, whether that photo was taken on the day the incident occured). It's what happened. Did any of the pax sitting in the vicinity of the woman in the terminal or on the plane, complain?? If so, then I feel the hosties were within their rights to ask her to show some decorum and cover up.
People get tattoo's for all number of reasons - whether it's self-confidence, to obtain attention from others (good or bad, they are still attentionn), to portray an image to others (whether it be things like toughness, or even the tasteful ones that I have seen women wearing from time to time in magazines, in real life or on the internet).
Do I have tattoo's - no, neither does my wife nor any of my family. However I know friends who have them and respect their reasons for getting them. They just wouldn't get me ruining the fabric of my skin for eternity. Each to their own...via la difference.