Is it possible that those petroglyphs are themselves graffiti ?? With plenty of complaints about defacing natural rock beauty...?? And we just think they are cool because they are really really old..
You can choose to see these petroglyphs however you want to see them. Certainly, it makes no difference to me and I wouldn't dream of trying to convince you otherwise. What I would hope you can see is that do they mean a lot to others and if nothing else, should be respected for that. If what others think means nothing to you, I should remind you that these petroglyphs are on federal land and protected by the law.