By 1931 they had won 6 league title, were runners up 6 times, had won the FA Cup 6 times and had been runners up twice. Which side between 1889 and 1931 (42 years) can lay claim to having achieved more?
Unless an individual player is quite clearly giving less than 100% then no proper supporter would ever boo their own player. Any that do are idiots as it doesnt help the players.