I don't think being a good person ought to require justification. It's almost part of the definition of something being good to not need justification.

But that's not particularly persuasive. So something I've been thinking about is why being a good person matters. In particular, I'm trying to think of an argument persuasive enough to affect the opinion of someone who doesn't already believe that being a good person matters.

Here's what I don't think is persuasive:

• "Because, God" - Theological guidance for moral behavior is a fine reason for being good, and I happen to be influenced by it. That said, there are a lot of people who range from ambivalent toward religious perspectives or downright resistant to them. Consequently, religious and theological arguments aren't sufficiently persuasive.
• "Because, it feels good" - To me, acting with goodness feels light, natural. It feels right. I feel good after doing the right thing, especially after a particularly difficult dilemma. But this isn't persuasive, because the spoils that can come from not doing good - and the power that comes with it - can also feel good.
• "Because, other people will respect me" - Sure, people whose respect is worth earning (in my humble opinion) will respect you for being a good person. But, if you switch your peer group you can get respect (cheaply) just as easily, so again - not persuasive.

Here's what I think is persuasive:

Let's consider a world where people generally act with goodness versus a world where people generally don't.

In both worlds, there is conflict. In both worlds, there is suffering (because even good people make mistakes). In both worlds, there is law and order (because we are sufficiently different from each other for misunderstandings to occur).

What I suspect would be different is the design of the governing institutions in the world where people generally don't act with goodness. There would have to be more laws, with steeper punishments, precisely because it can be expected that there are bad people. In that world, non-good people are not the exception, they are the norm.

As a result, there would have to be stronger components of law enforcement. There would have to be larger armies. The state would have to be strong, to prevent people from causing harm toward each other, more so than the world where goodness was the norm.

This is all to say that the state (or some other regulating entity) would amass power. Which is to say that those in cohoots with the state would also amass power. And as human history suggests when power is amassed by a select few, freedom becomes precarious.

So here's the most persuasive argument I can think of for being a good person. A society in which people act with goodness creates less of a need for strong, forceful institutions. Fewer strong, forceful institutions make it less likely that freedom will deteriorate. Because nearly everyone I can think of values a free society, we should be good and expect others to be good.

Goodness creates the space for free societies to exist.