Which parks specifically Jennifer? Because if you've got the misconception that guns aren't allowed in all national/state parks, you're grossly misinformed.
This has been covered before, but there's a lot of misinformation about where guns, concealed or otherwise are or are not allowed.
In most (if not all?) cases, firearms are allowed in national parks, as long as the carriers comply with local laws concerning such transportation. In most places in the country, open carry of firearms is completely legal, regardless of how rarely it's practiced. Generally, concealed carry however is restricted by permit.
For instance, in North Carolina where I live, not only is open carry unrestricted (however rare), you're even completely within your rights to carry a loaded handgun into a bank, so long as you aren't brandishing it, or attempting to commit a crime. The act of carrying the gun, isn't however a crime, so long as it's a legally owned firearm. Is it wise? No, only due to the inherent risk to yourself. It is however, an exercise of your constitutional rights.
I run into people open carrying pretty regularly on NC and GA trails. They've always been quite amiable.
There are even laws allow non-permit concealed carry in campsites, which are considered temporary residence.
If you've been passing hikers all this time without worrying, why start now?