To be honest, I was pleased when the heckler was pulled away by the two men. Of course, what they did can be counted as assault.
I'm not saying that the heckler shouldn't be allowed his opinion - or any of those people who criticised the Queen's funeral and/or the royal family. However it was the wrong time and wrong place.
If someone you knew was mourning the death of a person you didn't like, to tell them that before the funeral would be unkind, insensitive and downright rude. All the "anti" complaints could have waited until the rest of us had finished mourning the loss of someone we respected.