Bryan Caplan in Parenthood as the Trump of All Past Regret explains: whatever tiny alterations he makes to his life before he had his children, would result in him not having the precise children he has today whom he so dearly loves, and therefore he does not regret a thing.
This is seems to me like an entirely wrong use of regret. I think regret is useful when it suggests how you could have done otherwise, when having different such behavioral policy consistently leads to better results in structurally similar situations.
It's not exactly like the mistake of thinking that chaos theory should suggest you pay attention to every little thing in life. There the mistake was to think you could reliably and precisely enough predict how the little things being different leads to outcomes being different. Bryan is thinking about a very specific outcome in his life which he already knows has come to pass. He is counterfactually considering how it would not have been if everything in his past were not exactly as they were.
But given determinism, everything is already decided. This does not rule out free will, but it does suggest a proper use for counterfactuals. According to Vladimir Nesov: The meaning of a thing is how you should be influenced by it (the most succinct expression of LW philosophy imho). According to Gary Drescher: Why should you consider alternatives when making a decision, given that your ultimate actions are already determined? Because counterfactually-speaking if you did not consider such alternatives, you wouldn't have decided the way you did. So the use of counterfactuals, and in particular regret, is for us deciding how to behave. I don't see how Caplan's regret makes use of this.
And of course, there are other aesthetic uses to counterfactuals. Fiction, to take an obvious example. But am I missing something here in thinking that Bryan's regret is quite useless?