Personally, I don't think the tattoo's are stupid. Personally, I'm kind of 'iffy' about them being ugly, but they're not stupid, in my opinion. They serve a definite purpose, to Karla, and the/her story line. They openly display, and reinforce, her absolute worship of the 'superior white man', as well as her own inferiority to them. Regardless of whether it's indoctrination, or her own personal fetish (or possibly a combination of both), that's made her this way, she is this way. She believes it, it feeds her mindset, it feeds her sexuality and in an ambiguous way, it makes her happy. Meaning that, regardless of our subjective view of their beauty, they are at the very least functional, and in my opinion a furtherance to her identity.
TLDR: They may be ugly, but they're not stupid.