This is interesting, "When it causes more harm." Is it more harm now and also harm for the future? Or is it more harm now and it would provide benefit in the future? This is an interesting point when we use our speech. Is our intention actually for the benefit in the long run? Or is our intention just that we are going to cause harm now and it will stay harmful later? The classic example of something that is harmful in the moment but is not in the future is when you get a splinter in your arm, or hand anywhere, a big splinter. You take a needle and jab it in there and it hurts, you dig it out and you get that splinter out. It hurts in a short time but in the long time it's important. If you leave it in it will hurt and even more get infected.
At times, when you say something that seemingly is harmful in the present moment but if our intention is actually to alleviate long term pain then it might be okay to say it. However, if our words cause more harm now and more harm in the future then it's often better to remain silent.