I think you're still not understanding the dynamic between children and parents these days.
Things are not how they were 30 years ago. Children are exposed to a myriad of information on a myriad number of ideas in a myriad number of ways every day of their lives. Here's the reality of being a parent today, your children will have set ideas about many many topics long before they would ever speak to you about it. So the idea that a child would come out of their room, or come home from their friends house, or from practice or whatever, and ask you about the weighty issues of the day, is fundamentally flawed. Children will Google it. Whatever more they need to know will come from their friends via snapchat.
Here's the bad news for all the new parents out there, YOU, will be the last person they will ask about anything like that. And they will attach the least importance to your opinion. (And they will attach no importance to your opinion if your opinion deviates from information on Google or Wikipedia).
Does this mean you will have no impact on your child's development of ideas? No. But it does mean that you have to set your expectations reasonably. The combative and argumentative parent-child relationships in my own opinion, usually arise due to parents not having a realistic set of expectations in this regard.
As a parent, you have to adapt to this new reality. I'm not going to tell people how to parent in the new reality, or even in the old reality. But I will say this, launching into a lecture about the importance of free speech is a REALLY good way to lose the room when dealing with kids. (A lecture sounding speech on anything is a good way to lose the room.)
Or maybe lectures do work for some kids. And maybe there are some kids out there who talk to their parents about these things instead of simply googling them. But my last kid is going to college next year, and that was never my experience.
As I said initially, I really don't think that the scenario that you are envisioning, would happen very often in today's America. Kids today will already have these sorts of ideas set long before you even think to talk with them about it.
(And if that's too much for prospective parents to think about, I won't even let you in on the fun that awaits with respect to the subject of sex, or drugs.)