It's my business that children are born with fetal alcohol syndrome or test positive for meth at birth. It's my business that some addict neglects his/her children, or endangers his/her children because of chemical dependency. The reasons that someone else's addiction is my business are many. 
I wouldn't care if an adult wants to snort or inject or smoke or drink whatever substance they desire - but the destruction they leave in their wake affects all of us.