What's the purpose of blocking someone when they unfriended you?

I unfriended because I saw something he posted that didn't sit right with me that I'm sure he didn't think I'd see so instead of wasting my breath I unfriended him. He sent me a lengthy text explaining how he was a good guy and all this. I was going to reply back but he had blocked me. What's the point of defending yourself at this point and then blocking someone?

What's the purpose of blocking someone when they unfriended you?
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