I need to figure out modal logic

I need to figure out modal logic, the language of expressing objective truth: It will look like this: I think, therefore I am i.e. I'm experiencing consciousness, therefore I know I exist. I also know other beings exist along with me, and of all of them, only 2% decide not to be here (suicide). Therefore I know existence is good/positive otherwise humanity would have ceased to exist for the majority of beings deciding to not exist. In metaphor if existence is a theatre, the house is always packed.

If existence is good then harm is defined by unnecessary actions/inactions thwarting existence. Once harm is identified under that rubric, all moral arguments are brought from any subjectivity into objectivity--where is the harm occurring, and does it harm existence, which is good.