I can also see how this can go wrong because as you suggest it can become the whole of a person's identity or the diagnosis can become a sort of badge, people being proud to be ill or something.

I guess it kind of depends on how you look at it. When I came across this issue, I started to think that people might already know (or think they know) a lot about you from knowing you from before or what you wear or your skin color or your scars, and judge you as they please.

So a tattoo is not going to hide the rest of your identity, but simply bring a certain internal fight you had been fighting all alone, to the surface, almost in a way to being proud of the surviving so much pain and misery, of your willpower, your strength. Being proud enough to show the world. It's anti-shame. It's also to offer support to other people going through this or people who have lost someone. So there is a sense of community from this shared suffering. So those aspects can be positive in my view.