I walked in with my first airsoft gun, plopped it down on the couch mom screamed at me yelled at me all that fun loving stuff...
... Only because she thought it was real
Still was pretty pissed about airsoft, but I kept to it told her I'm not giving up something I love that is not harmful to me and what not.
Now she's meh accepting of it.
Years of work, keep at it!.
Or, get a local rep to maybe see if he'll stop by and talk to your parents about it, see if he can help or shine some light on this demonic, unholy satan loving sport