One of the cool things my parents did for me when I was growing up as a T1D was never letting me know it. No special privileges and no special restrictions. On Halloween, I’d get extra insulin so I could eat some of the candy. (This backfired one time when I didn’t eat any…)
If you need a pass, get one and use it. Just like a handicap parking sticker for a car. Nobody would fault someone for that.
But if you don’t need it - if diabetes is not a disability for you, then getting one will only start to reinforce the idea that diabetes is a disability. And I think that is an unfortunate thing to do for the sake of saving a few bucks to get into a park.