That certainly depends on whether you are on the paying or the receiving end of the blockchain scam. For one of them it works really well ...

The overall mantra of this book is: Don't reimplement database features in your application that the dbms can do for you. I really strongly agree with this, and even if you don't recall any of the concrete recipes in this book then this mantra will hopefully stick.

Don't make it a hard rule, though. There are exceptions to everything. Sometimes it's easier, faster or more flexible in the client.

The criticism is that it's not honest. "For free" is not correct. It's "book against harvesting your contact data". If that's what the first page would say, then it would be honest and nobody would be upset. But acting as if it's been "published" out of pure altruism is just misleading people, and they are righfully pointing that out.

I took it to mean “free as in beer”

Would you pay money in lieu of providing your real email address? If so, how much?

I’d probably pay $10, that’s worth less to me than my contact info.

Just use a throwaway mail, what's the big deal? Companies already have tons of your private data without you ever even interacting with them. You're just crying into a 50 gallon drum of milk.

A whole bunch of burner addresses of people who are hoping to one day be db pros must be REALLY valuable.