Is there any reason to think this is the case? In my experience, in-person disagreements over 'big things' (be they politics or philosophy) either end in bitter disagreement, or what appears to be a compromise but actually isn't (because one or both parties do not wish to talk about the topic any more, before things get worse).
> However if one side of the discussion is self-censoring, then both sides will tend to develop extreme opinions without any means to tamper them.
This assumes that most disagreements are resolved when there is a difference of opinion. Personally, I rarely change my opinion after speaking to someone, and I instead change it when I do my own reading around topics. The fact is that it's awkward to ask 'what's your source for that?' in a conversation between friends. Either one or both parties don't care enough to provide a source, or it's impractical (such as at a dinner party).
To surmise, I'm questioning whether mere in-person disagreement really does tamper the essence of those extreme opinions, not merely the appearance presented to that particular conversation partner.