Mr Welby said he was “shocked” by Mr Johnson’s recent dismissal of concerns extreme language could encourage death threats against politicians as “humbug”.
And he added political leaders could no longer behave the same way as Mr Johnson’s hero, Winston Churchill.
“Churchill was well known for his somewhat inflammatory putdowns in parliament,” the archbishop said. “But this is happening at a time when we have social media, which amplifies things.
“In a time of deep uncertainty, a much smaller amount of petrol is a much more dangerous thing than it was in a time when people were secure.
“There is a great danger to doing it when we’re already in a very polarised and volatile situation.”
Mr Welby said action was needed to heal divisions “at almost every level of society, including the political level of society”, adding: “I don’t only blame government. I think we are quite broken.”