His insomnia, his means of method acting, and his taking non-prescription drugs against his doctor’s orders are more likely candidates for his demise: https://www.quora.com/Did-his-role-as-the-Joker-drive-Heath-Ledger-to-his-death-Was-the-role-too-challenging-and-harmful-for-the-actors-psyche-or-sanity
There have been objectively more immoral/crazed roles in film history than Ledger’s Joker, yet those actore didn’t go on to overdose on medication (Hannibal Lecter comes to mind). To blame his death on a singular movie role is to ignore the other factors.
There are even more people on Heath Ledger’s position now...with the opioid epidemic and everything...and more mass shootings since then. Why create content that enables people’s (and greater culture/society’s) demise?
Hollywood is sick. And so is America.