Why does harry accuse Remus Lupin of being a coward?

I would say yes. He father Luicus was disliked by the greatest Dark wizard of all time, and Lord Voldemort had no problem killing anyone. Draco was just acting brave to save his own life. His job was to kill Dumbledore, but he was to chicken to fulfill that order so Snape have to cover for him. There is proof in the last book also, but I don't want to ruin it for anyone.