There are few movies that have had that kind of lasting impact after watching it. Regardless of what theories you may have on this or that, it does something more profound and lasting. It forces you to look at your fellow human being and his plight, and moves you to compassion. To understand the suffering of the other and to take a moment to offer help or console.
This movie is controversial simply because it makes you understand and sympathize with the monster. And it offers a visceral understanding of why the disturbed and destitute have committed acts of late.
You want to see Joker in real life, go to California and spend some time with the homeless and mentally ill roaming its streets. As a society we need to attend and help these folks. There is where the real crisis and our biggest failing is taking place, and like the Joker, it is nothing to laugh about.