>Why should I act morally?
To be a moral person. It's that simple. If you have no desire to be moral, then morality has nothing to offer you. That does not mean morality can't be applied to you, though. Whether you accept morality or not, everyone else can still judge you on whether you are moral or not. Moral judgement can be expressed in positive statements just fine; in fact, I'd argue that there is no great divide between normative and positive statements. All "should" statements imply a conditional. "You shouldn't jump off that cliff… if you don't want to die"; "You shouldn't kill another human being… if you want to behave morally", and so on. Those can be stated in a positive way, too: "If you jump off that cliff, you will die"; "If you kill another human being, you are not behaving morally".
Which system of ethics is the right one, and how to discern that, is a question for another thread.
>>18512
>there is no such thing as good or evil. they are just arbitrary concepts. imagined by somebody, repeated by others.
That someone invented a concept does not make that concept arbitrary. Mathematics is a concept, and it isn't arbitrary. The scientific method is a concept, and it isn't arbitrary, either. Likewise, there is nothing arbitrary about a coherent system of ethics, either.