Assuming incompetence instead of malice is how you remain collegiate and cordial with others.

Assuming malice from people you interact with means dividing your community into smaller and smaller groups, each suspicious of the other.

Assuming malice from an out group who have regularly demonstrated their willingness to cause harm doesn’t have that problem.

From parent's comment

> It doesn't encourage the need to reason, examine any evidence, or examine any probabilities

Parent isn't advocating for assuming malice, or assuming anything really, but to reason about the causes. Basically, that we'd have better discourse if no axiom was used in the first place.