Why should you be so suspicious?

你何必多疑？

《新英汉大辞典》

Al: Don't be so suspicious, I really meant it.

艾尔：别那么多疑。我是衷心的。

youdao

He's so suspicious he would distrust his own mother.

他这人疑心太重，连自己的母亲也不相信。

youdao

"So you have to surveil them a long time until you can say 'okay,maybe he's kind of a suspicious person, so maybe we should investigate it a longer time or not.'

VOA: standard.2010.07.27

They were very suspicious of the democratic tendencies, or so it seemed, the democratic tendencies of that northern society which was spreading literacy more widely, and eventually the right to vote more widely, at least among white people.

他们也对民主倾向表示怀疑,事实就是如此,有着民主倾向的北方社会,文化教育的开展更为广泛,因而更广大人民有着投票权,至少大部分白人有投票权

耶鲁公开课 - 美国内战与重建课程节选

And, it has to be allowed, the behaviour of the So San was suspicious.

ECONOMIST: Drama and farce on the high seas

Police officers say it is suspicious that so many single young men should be staying together though they all say they are tourists or businessmen.

BBC: Sri Lanka - hub for human trafficking

"Gold doesn't produce any income or have a yield, and you have to pay to store it, so people are still suspicious of it, " said John Griswold, executive director of Commonfund Institute.

WSJ: Gold's Fall Stings Texas Universities' Endowment