There are I think two other related aspects that are relevant. First, there's some tendency to interpret what other people say in a highly non-charitable or anti-charitable fashion when one already disagrees with them about something. So a principle of charity helps to counteract that. Second, even when one is using a non-silent charity principle, it can if one is not careful, come across as condescending, so it is important to phrase it in a way that minimizes those issues.