Honestly, Robin can work in a movie. People, fans and writers alike, just cling to the idea that if they use Robin "everyone will think he's gay with Batman" or he takes away from Batman's "seriousness". They're excuses at the end of the day.
I doubt we'd ever see it, but I'd love to see a Batman franchise that embraces the Batfamily at large, giving us Batman, Robin, Nightwing, Oracle (or Babs as Batgirl), and others. The comics themselves even drive home the point that for all his talk and reputation as a "brooding loner", Batman actually has a close knit team of people he considers family.
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Robin can totally work provided there is a total revamp. I'm really drawn to the hooded robin look from arkham city. If i was to add robin to a batman movie I would seriously consider the hooded look & I would try and change his costume to look more like Ezio Auditore from Assassins Creed, but obliviously with darker red colours. Finally the character would have to be shadowy, dark & spooky. It could totally work. Check out my attachment and have a think about it.