I agree with @luc and @evan.ward. To be honest, I never ask myself whether I should squash commits. Even if, like everyone else, I can be a bit messy in this regard, I assume that they are thematic. By leaving them as they are, we reduce the number of lines to analyze when we manage to associate a regression with a commit.
As Evan says, I think it makes more sense to teach all contributors how to manage their commits properly and encourage them to exercise self-discipline.
And above all, let’s teach everyone the virtues of the git add -p command, which saves people like me who are a bit messy on a daily basis. 