No, they shouldn't. Here's 5 reasons why.
1. It's disrespectful...
If people think that including any JLA member without a big role is good, they are quite wrong. Flash and Green Lantern deserve their own movies and they may not have many appearances but they are popular enough to earn more than $700 million if the movies are good. It is kind of disrespectful that they have to take help from [Batman vs. Superman](movie:711870) if they want entry to the big screen.
2. What are the sidekicks for?
Batman has a pretty awesome team where we have so many options to choose from: Nightwing (Dick Grayson), Red Robin (Tim Drake), Robin (Damian Wayne), Batgirl (Barbara Gordon) or Red hood (Jason Todd; maybe not him, he is not so popular). They all need a big screen appearance and it is the perfect opportunity to do this. So, instead of overcrowding a single movie with so many heroes, it is better to give a chance to sidekicks.
3. Superman has got some hands behind him too...
Superman has got some friends of his too: Supergirl, Superboy (Connor Kent) or Eradicator. People don't know much about eradicator but i think I am the only one who has spotted the possible Easter egg for Eradicator in Man of steel. Eradicator is the personification of Fortress of Solitude and later becomes a superhero in his own right. By Easter egg I mean the dead kryptonian Clark Kent sees in Fortress of Solitude could have been Eradicator.
4. Who's the boss?
The better question is that Who is the idiot? Zack Snyder thinks that only he is capable of making DC superhero films and he's already shifted the release date of Batman vs. Superman initially from 2014 to summer 2016. There should be more directors to bring other DC properties to big screen by not overcrowding movies which are not supposed to be Justice League. Snyder says he has a different vision but then he should share that vision. It seems bad when Marvel releases 3 movies a year while DC releases a movie in 3 years.
5. Overshadowed performances
With so many actors in lead cast, no one can share equal screen space and won't be able to give a good performance.
What do you think of my reasons? Hit me up in the comments below!