I'm convinced...
...that Zack Snyder is actively trying to ruin DC's movie universe. How else to explain his horrible casting choices -- with the exception of Affleck who I always thought would take the role seriously and be excellent in the part. Ezra Miller comes across as such a lightweight that I just don't see him being able to anchor a franchise like the Flash.
Snyder has previously made some wrongheaded casting choices: Sarah Polley for DAWN OF THE DEAD (good actress but not dynamic enough as a film presence to be a movie heroine); Emily Browning in SUCKER PUNCH (see Sarah Polley), but he did have the perfect actress in the movie to play the lead -- Jena Malone -- but stupidly made her a supporting character, though I doubt any actress could've saved that mess of a movie; and Malin Akerman in WATCHMEN, her performance is so Godawful and clueless that it nearly ruins the entire movie.
I can't believe Warner Bros. thought it was a good idea to place these films in the hands of a hack like Snyder. It was a license to print money in perpetuity and they've bungled it horribly. They've made money, but alienated the support and goodwill of millions of people who wanted to love these movies.