does karma exist?

I believe in karma (especially bad karma) not because I truly believe in its existence, but because I believe in the good it could bring to many people if there would be a lot of people who'd believe in it and thus would apply said belief. I just know that anything bad I do to another would come back to me sooner or later (bad karma). Knowing that bad karma thus exist would make others be cautious about hurting others. It would also make us think twice or thrice before doing something. This could make the world a better place to live in.