Just because "everyone else does it" doesn't mean you should "hop on the bandwagon" and engage in data collection from your instance, including email addresses to spam instance owners without opt-out links, and ultimately using that data to engage in data collection research studies without consent.
In my opinion, this type of behavior should be strictly double opt-in for the sake of end-user consent, just like unsolicited email. Not allowing to opt-out is, again, unsavory at best.
@keith
Morning Keith, hope you're well. I think it's best to reply to all three of your comments that came in overnight here.
We reached out to the bookstodon team using the public email for your instance because you're one of a few dozen Fedi folks we thought would be interested. You've clearly opted out and we respect that. We won't email you again and we have already opted out bookstodon.com from future research.