Facebook has an opt-in mechanism called "signing up for a Facebook account." G+'s equivalent is "signing up for an unrelated service, possibly as long as a decade ago."
How do I use Facebook Chat and Facebook Photos without a Facebook News Feed account, and without Facebook Like buttons recording every web page I visit?
I think the disconnect here is that people don't seem to
get that "I voluntarily signed up for a social network" is an important step for a lot of people. It's entirely possible that a lot of people who hate g+ now wouldn't have minded it if it came out of the ether right after Facebook got popular, instead of being retrofitted onto something that already existed and foisted on that userbase above its protests. You can't just unilaterally change the purpose of your site and expect people who liked the old site to automatically like the new one.
FWIW, I also hate Facebook Connect and refuse to use it on principle despite having a Facebook account I voluntarily use.
I declined G+ for a while, but eventually pressed a button and consented to convert my accounts. I am not aware of any automatic conversion, especially from 10-year-old accounts. I assure you, my Gmail account is older than that.
Either it stops being optional after some point, or they tricked me into converting vis-a-vis some Dark Pattern (which is if anything even more scummy as far as I'm concerned). My YouTube account is separate from my Gmail account and I can assure you that I never would have added a g+ page to it on purpose given the choice.