There is a very strong tendency to form opinions about people based on very little information. I've been on the receiving end and I've done it myself. I'm pretty sure we've all been guilty from time to time.
Some people are on the receiving end more often than others. People who dress differently from the people around them, people with facial piercings, and people with more than a couple of tattoos -- all tend to be judged based on appearance. I don't think they appreciate it. You might think they'd be a little more careful about judging others - but you might just be wrong about that.
My daughter-in-law is tandem nursing her 2 young children. She wanted to celebrate her breastfeeding success with a tattoo of the international breastfeeding logo. Hers is a little different from the one in the link - red, heart-shaped background and her babies' initials on either side. As the image was being completed, one of the other artists in the shop came over to have a look. He asked her the significance of the image and when she finished explaining, he said, "You're not one of those fanatics who breastfeeds their kids for 10 years, are you?"
I'm obstinate enough that I'd have said yes without thinking about it. She opted for a more moderate answer and told him she plans to breastfeed for 2 years. She'll really breastfeed for as long as the kids need it. She said she didn't feel like being judged by someone who'd chosen have most of his visible skin covered in tattoos.