French politics is very stable. Your leaders tend to be all very similar, at least in recent years. Macron is not wildly different to Hollande etc.

Despite that, France routinely sees a lot of remarkably aggressive political activism - farmers dumping manure on roads, the incident with the fishermen pelting the boat with rocks a few days ago, huge quantities of striking and so on.

I don't think there's anything special about France that makes French people able to discuss politics in a more civilised way. If France were to see significant change in politics the discussions would stop being 'adult' very quickly. For example if you had a referendum and France voted to leave the EU, "Frexit" would rapidly turn into a much more heated topic than it is even in the UK, I bet. It's all about the stakes.

I wish this was more common here in the States, but it just isn't there. It's becoming more and more difficult for adults to disagree without slinging insults at and hating the opponent. We're an incredibly politically divided country right now and political beliefs are held as immutable core parts of our identities instead of strongly held beliefs subject to change, so people who disagree with you are considered to be attacking your identity.