I have never, ever met a person who got a tattoo because they wanted to be unique or different. And I have met tons of people who have tattoos. The people I know who have tattoos got them because the design holds special meaning, or they wish to honor something or somebody, or because they like the design, or for tons of other reasons as well. But never have I met someone who thought that having a tattoo would them unique, or cool, or whatever.
For the people I know, a tattoo is not something they just rush out and get. Tattoos are permanent, and hold very special meaning, and they can make months to plan out the design of their tattoo.
I know I'll get a tattoo some day, I've wanted one since I was 13. But the reason I haven't gotten one, in the 10 years I've been wanting one, is because a tattoo is permanent, and I haven't come up with the right design that will mean something to me. It takes time, and patience, because it's in your skin for life.
A tattoo is very personal, and yes the picture might only be skin deep, but the meaning is as deep as the very core of your being. And the cost for tattoos and piercings is no more obscene than someone spending $1600 a year to get the newest Ego every time one comes out. Or someone paying $40,000 for the car he's always wanted. Or any other way that people spend a lot of money. The only difference is that the Ego might last what, 10 years, max? And the car might last 15? But that tattoo will last for the rest of your life.
It's a way for an individual to express themselves, the same as kids buying expensive clothes, or expensive electronics, or styling their hair a certain way. It's an expression of themselves and tells a story about who they are, where they've been and what they've done.
So just because you don't see the significance or symbolism of a tattoo, doesn't mean it doesn't exist, or that it's because people want to be unique, or whatever other reasons you might come up with to put down someone who chooses to express themselves in a more permanent way.
I really don't see the reason why you would feel the need to be so negative towards someone who has a view different than your own. Just because it's different, doesn't mean it's wrong. You don't have to agree with it, but that doesn't mean you have to be rude when you disagree.
Now, granted, there are the idiots who rush out and get a tattoo and then regret it later, but I tend not to associate with those people. I merely described reasons similar to the reasons as to why I myself, and some of my friends, have gotten or will get tattoos.