on principle
as a moral matter按道理；原则上
He drinks a cup of hot milk every night on principle．他每晚照例喝一杯热牛奶。
I dislike going out for meals in restaurants on principle； why should you pay so much money for food that you could prepare yourself？我就是不喜欢去外面餐馆吃饭，干吗要花那么多钱去买那些自己能做的食物呢？