With the influx of comic book movies lately, it does seem to beg the question of "Do we need to start picking up the comics to get an idea of the characters?" When I saw the original The Avengers, I hadn't seen either Thor or Captain America, and it had been years since I saw the Hulk tie-in movie. It didn't make me confused, I was still able to enjoy the characters and the story, but there seems to be a stigmatism lately that you have to at least keep up with at least 4 different movies to go in and see one.
This same thing happens with books to movie, where a lot is left out and then you feel silly for not knowing about something while someone sits there and tells you to just "Read the book". The problem with that where comic books are concerned, however, are there are so many different origins of all of the superheroes, different mythos and many different subsections that it is hard to know where to begin. Not to mention the TV shows that spawned their own ideas (Harley Quinn is the child of Batman the Animated Series and was only added into comics after her growing popularity)
You have the purests, who think that The Joker having tattoos on his face is absorbed and just too farfetched, when really the idea is just a new reimagining of the character. While I, myself, am a huge fan of the original Harley, the new look doesn't completely offend me because it is an update on the times
I have seen many people getting into it on whether you should read the books, or the comics, and that you are less of a fan if you don't, but that kind of thing adds up, whether it's shelf space, money, or time. While it's easy to have those things when you are young the older you get it's harder to keep up. Media is an outlet, of viewing, of speaking your mind and of meeting other people. Instead of judging or getting frustrated, maybe it would be nicer to educate someone if they want it or just walk away.
Leave the back story for origin movies, or the exposition fairy to go over in the film and just be happy. You are a fan seeing your work on the screen and someone else may be joining your fandom.
Nobody is less of a fan for not knowing that Superman once had a dog named Krypto