He used a phrase I hate: "You have to be cruel to be kind."

他用了一句我讨厌的习语：“要想善良，就得残忍。”

《柯林斯英汉双解大词典》

We shouldn't be cruel to animals.

我们不应该对动物残忍。

youdao

As long as humans are cruel to animals, they will be cruel to each other.

只要人类对动物残酷，他们必然彼此残忍。

youdao

They were very cruel. I thought,perhaps this beast can be taught to be my friend...

VOA: special.2010.07.17

And this is line 679: Why should you be so cruel to yourself, And to those dainty limbs which nature lent For gentle usage and soft delicacy?

在第679行：，你为什么要对自己那么残忍，对于大自然赋予我们的四肢,只文雅的使用和温和的对待佳肴？

耶鲁公开课 - 弥尔顿课程节选

The message of the flood story also seems to be that when humans destroy the moral basis of society, when they are violent or cruel or unkind, they endanger the very existence of that society.

而洪水所表达的信息是,当人类毁掉了社会的道德根基，当人类变得暴力，残忍，这都会危及到人类社会的存在。

耶鲁公开课 - 旧约导论课程节选

It would also be cruel to run brain scans on someone who was possibly facing the moment of death.

CNN: SHARE THIS

Instead of forcing us to replicate long swipe gestures using a mouse (which would be cruel to all concerned), Microsoft is putting forward these little key combos as the primary means of navigation on traditional desktop PCs that don't have touchscreens.

ENGADGET: Windows 8 upgrade diary: multiple monitors make my mouse mad

Why do they have to be so cruel to the families that are here?

CNN: 'Rogue' DHS unions follow Obama's lead on deportation