The interviewer is not evaluating your old company. To the extent that the interviewer asks, they are trying to find out about you. The interviewer at WidgetsCo doesn't care at all about the work environment at FlibbetsCo unless he's thinking about interviewing there himself or he's considering poaching some employees. If the interviewer at WidgetsCo asks "why are you leaving Flibbets?", he's actually trying to find out if there's a problem with you.

If you want to speak up at your current employer to resolve issues, I would generally encourage that. There's clear value in being honest with your employer and trying to work out issues (though there can also be risk if you have a really unhealthy relationship with management). Being "honest" with an interviewer about your current company doesn't solve anything. You won't fix problems with your current employer by telling a new company about them. You won't likely discover anything useful about the new company. And they won't likely learn anything useful about you, because it's impossible for them to tell if you're just bitter and spiteful or if you had legitimate problems caused by the company.