1. wouldn’t dream of = wouldn’t even remotely think of/ wouldn’t do because you think it is wrong or silly.

• Even if it were lying open on my desk, I wouldn’t dream of reading another person’s letter.
• My father is very generous , but I wouldn’t dream of actually asking him for money.

2. Lead someone astray = cause someone to act or think foolishly or wrongly.

• I’m afraid that this young man has been leading you astray.
• Nobody can lead him astray.

3. Necessary evil = An evil that must be allowed for greater good to result. (Necessary evil may refer to the ‘lesser’ in the ‘ the lesser of two evils’ principle.)

• These days, student loans are a necessary evil in order to get an education that leads to a well-paying job.
• Most Americans accept taxes as a necessary evil.