Spin the story however you want, the key features were 'drunk' and 'emotionally vulnerable'.

Although the former should have been enough given my first example: "too intoxicated to stand, remember what they were doing half a minute ago, but are just about able to slur our the word 'yes'"

Someone who tattooed a willing person whilst that drunk would be in legal trouble because it wouldn't have met the standard of consent required for tattooing someone. Apparently you agree that having sex with someone in that state is unethical, but the standard for consent in sexual relationships that you want to advocate is basically just 'willingness' all by itself.