You're Too Old For That Book

We have entered banned books week!  And for this post, I want to talk a little about a different kind of restriction.  My friend and I used to hang out a lot at the Greenbelt Mall.  (Ah, good times.)  And so when they added what looked like some sort of middle ground between a Chuck E Cheese and a Dave and Busters we were excited.  Now this was partly because this mall had limited food selections, unless one wanted to eat at the movie theater or the ice cream shop, and while certainly the greater Greenbelt/College Park area had a plethora of fast food choices, variety was always welcome.  (There were also non-fast food options afoot, our budgets were pretty firmly fast food most days.) Well, you can imagine our sadness to discover the pizza offerings at this new arcade and games joint were not available to us since we did not come with children.  Now, yes, I understand that sadly, some adults might be drawn to such and establishment sans their own children for nefarious purposes, and, yes, I want people's kids to be safe.  But my friend and I could not figure out why we couldn't play the games (through the windows it appeared, other than the ball pit, adults could partake in all of the games) or eat the food.  But no. 
But, it seems, as an avid reader of YA and the occasional middle grade (MG) book that letting me take out books from the library poses no risk.  Certainly, in a surfeit of cautiousness I could see why libraries might want to restrict kids areas from unattached adults, but I have to tell you I, kidless (not even a babysitting charge in sight) had the pleasure of hearing Flat Stanley read aloud by the author (although my mom was with me, does that count, even though I was fully grown?) and it was awesome.  And certainly I understand that libraries budgets are crunched (assuming they still have one to speak of) so if first priority for books aimed at kids went to kids, I'd be all for that.  But if a book is in the library and I cannot get it out because I am too old - well, I have to ask why?  Why is my reading something aimed at a different age group an undesirable thing?  Why should I have to produce proof of child to do this? 
When this came up on Twitter the issue of teachers was raised.  (In fact the person who mentioned it was a teacher.)  But also, this makes shelving marketing decisions super crucial.  After all, with talk that books like Huckleberry Finn and Carrie would be (and sometimes are) shelved as YA today, so who decides if I am allowed to get that book out.  And again, I am stuck on the why. Could I be planning to lure innocent children with my excellent library lending?  Could I be getting terrible ideas from these teen books?  Will I use my broadened knowledge of texting and teen slang to annoy my co-workers?  (Okay, that's actually possible.)
The only thing I can come up with is some sort of mirror law type thing where someone has decided if kids are going to be restricted from some books then adults should also get restricted.  Seriously, don't make me get a fake ID to take a book out of the library.