What is the source for this reasoning
It's a mix of FUD and reality. If you want to post reviews on certain Google sites like Zagat or Google Play, you're going to need a Google+ profile to do it. Fact. The integrations will continue, that's another fact.
There are some really simple steps to take to avoid this auto sharing (which I think should have been opt-in)
1. The fastest way to stop it is to delete your Google account. Free and clear.
2. If you just want to stop public access to your profile, make it private, or adjust access to parts of your profile that you want kept private.
3. You can also delete your Google+ profile but keep everything else. You lose some features, but you might not care.
As for the FUD, do your own research and make your own choices. Fear mongering exists in all of these technology pissing matches, but don't react based on what someone else wants you to do.
If Google+ gives you the creeps but you want to keep your other Google access, see #3 above. If you want out altogether, see #1. It only takes a hot second to complete.