It is hard though not impossible to do this, because stumbling blocks of ego and pride await. It ought (and sometimes we fail) to be in the tone of “Here is a better way to do this” rather than “I berate you, you SOB.”
I agree with your basic premise and I know where you are coming from. But what you bring up is an interesting puzzle especially when looking at people of scripture as well as great Christians of history and how they approached things. This includes are Lord Jesus. At times our Lord was very gentle in His approach to others. At other times He was very critical. And, what is interesting, when you thought that He would give a gentle answer He would be very stern and visa versa.
I’m not sure if a “one sizes fits all” really works. I suspect that different approaches are what God uses to further His kingdom. This is very important when one thinks about how we approach witnessing and discussing the gospel with others. Some are more quiet and subdue while other are more aggressive. Some don’t have the foggiest idea of what they’re talking about while others are more thoughtful. In the end it doesn’t matter. We can trust the seeds of grace will always sprout whatever manure we place on top of them. :O)
In the end God gets His message out as He so promise, no matter how bad we may think we mess it up.