You're acting like the act of "joining" is some huge deal. You already have an account with Google. "Joining" Google+ probably flips 3 bits in some BigTable database somewhere. The only reason you are getting so self-righteous about it is because Google is giving you the option. If you don't _do_ anything on Google+, what's it matter?
Interesting that you bring up you Facebook anti-creds. Do you also not own a TV?
Joining IS a huge deal. Lots of things are getting shared when you have a Google+ account, most of which I don't want to share (e.g. which YouTube videos I like, my Google Play comments...) and have to be turned off explicitly. I know this because I once was a Google+ user for a short time (during which I didn't even notice).
When I mentioned Facebook I just meant: "I'm not into the biggest and most useful social network, why would I join your crappy-and-useless one?"
I have so far avoided combining my YouTube and Google Plus account. They keep annoying me with random overlay asking me to combine them but so far I've been saying not now. One way I've minimized exposure to this is using the android app instead of the desktop browser version but it may not be for everyone.
I probably don't need to tell you this but just in case: If you have a concern about a Play Store, please contact the developers and give them a chance to fix things. Thank you!
They started pulling that nonsense on me too. About every tenth video has an overlay and there is no "just leave me alone" option. I end up using an incognito tab instead. For the life of me I can't tell what choice they are trying to force me to make and what is wrong with how things are at the moment.
The overlay has changed a couple of times, when they've combined or relabeled the options. The last time I got it, they had removed the "go away" option, so I gave them one of the answers they accepted - "I don't want to use my g+ profile, because X".
Of course, about 30 seconds afterwards, I noticed that the option that actually was most accurate for my situation was Y, but I hadn't clicked on that, so whatever.
Because settings change. I don't know if tomorrow Google is going to add a new feature to share new things, and I don't want to watch for new things to opt out of. It's a cognitive load I don't need.
It's not "opt out once," it's opt out and monitor that your decision isn't "forgotten" at any point in the future in which case you need to opt out again. So, yeah, "continuous hidden opt out" is annoying.
Interesting that you bring up you Facebook anti-creds. Do you also not own a TV?