How does getting people to voluntarily sign up to receive emails about a topic that interests them compare AT ALL to buying scraped emails?

You are wrong, and I don't mean to sound insulting but it seems like you are making these comments on theory and not on experience.

I have multiple sites with pop-ups that see outstanding open and click-through rates, it's not even close to the same thing as buying an email list (which doesn't work, as you pointed out).