It's a great trailer, but (sharpen your knives!), it doesn't actually look like a great movie to me.
More importantly, I think the last one, and obviously this one, are dangerous for the public to consume. Sure, it's about how the world can beat up an average guy, and how mental disease is a thing, but it romanticizes the downward spiral into madness, murder, and mayhem. Someone down on his luck and somewhat susceptible to a violent lash out or breakdown, doesn't watch this and come away with something inspirational like what he might with Pursuit of Happyness for instance. It glorifies the wrong things and motivates vulnerable people to consider inflicting damage on the world and those around them.
I'm not a supporter of the playing violent video games leads to violence theory per se. In some situations, I'm sure it can be a factor, but along with many other contributing factors. It's also arguably an outlet, a safe way to live out fantasies in some form. But a movie like Joker isn't an outlet for anything really. It's something that can only stir up negative and harmful emotions. I suppose it can be said to draw attention to mental disease and tell normal people that more needs to be done to help society in that department, but it tells the not so normal people out there that everything is awful and hopeless and that the world has earned their vengeance.
Fire away.