Seems like people are focusing on their own personal inconveniences rather than the website as a whole (perhaps "private" didn't help heh). This site is free and was created "so that the community, the ecology, and the value, the economy, of comics have a place to exist." Maybe people against the idea of semi-privatization should re-read what Batoto stands for (or read for the first time if they haven't already): https://vatoto.com/forums/topic/1957-batoto-is/
So, back to Grumpy's concern which is REDUCING THE DEEP CRAWLS ON THIS WEBSITE. It's completely impossible to control all crawling. Absolutely impossible (some crawls are real everyday people). But if implementing a member's-only feature will make deep crawling a little more difficult, then I don't see an issue. Something has to be done otherwise this site will close and I'd hope that's something no current user wants.