What I mean by not being able to talk about them is that you can't express your honest opinions.
Most people probably think their boss is a jerk, that their colleagues are incompetent, that their company rips off their clients, so on and so forth. You can't say any of that with your name, and by extension that of your employer, attached to it.
The same applies to education. Teachers can no longer discuss teaching methods or lesson plans online, lest their pupils find out their teacher doesn't have a clue what they're teaching. Pupils can no longer criticise their schools online, or seek help with bullying.
The list of topics that people are willing to talk about pseudo-anonymously but not with their real name attached to their comments is endless.
> The message I'm teaching my kids is "only post things online that you would be comfortable seeing on the front page of the newspaper"
That's precisely the attitude I subscribe to, and it's why I don't have much sympathy for the teenagers who take photos of themselves scantily clad, put them on Facebook, only to have them end up on places like /r/jailbait.