I don’t think “Keep your feelings to yourself” was the message. If that is what you think, you completely missed the point of that letter.
The message was more along the lines of yes you have opinions, but so do others, they have the right to express them in a respectful manner, and you can either listen to what they have to say or you can walk away.
I don’t always agree with the opinions of my friends or family members on a range of subjects, from the inconsequential to the most sensitive, but I will not stop talking to my friends or my parents simply because we do not always agree. They are respectful in delivering their side, their opinions are educated, I get to see things from another perspective. It helps me to understand where they are coming from.