"Stupid idea" is indeed not constructive. "Will never work because [XYZ]" is constructive IMHO, although not very polite. Being Israeli I prefer brutal truths

"Stupid idea" is indeed not constructive. "Will never work because [XYZ]" is constructive IMHO, although not very polite. Being Israeli I prefer brutal truths over polite bullshit. And personally I try to be honest with people showing me their ideas - while being positive and polite. But knowing the scene, not all Israelis are like that.