Some people/religions count making any intentional changes to the body you were given as harming it... so maybe that's the line of thought? Like, I don't agree with it, but I understand the perspective.
The person that told me this is a nurse, and that wasn't her line of thought. She used to work in rehab with people who were recovering from addiction and just told me "Well, they shouldn't have chosen to use drugs in the first place." (we covered more than just tattoos as a topic, lol)
I also attempted to educate her that while *technically* you make the choice to use a substance, sometimes the genetic component makes it a bit less of a choice and sometimes you "choose" these actions so young to escape another painful reality (like you're 12 and have terribly abusive parents, so smoking a joint makes your reality a little better, and then next thing you're having a few drinks...and then...and then...)
She simplified it all to just people "being weak" and wanting to harm themselves.