Even though I agree this will likely help avoid spam, I don't like it. I have many different accounts on many different websites, and most of them I barely use. But when I come back to ask a question after 5 years, I don't want to have to jump through hoops to prove I am still me. I think this applies:
When barriers to participation are too high, then the best people often just won't go to the trouble of joining, and the people who are willing to jump through the hoops are often people who aren't good for the community: people with nothing better to do, scammers, get-rick-quickers, etc.
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