In my opinion down voting would never help. Users are simply going to down vote an idea when they find it inapplicable to their business or when they do not fully understand the idea. Lets just take a moment to review our experience on the forum where we constantly find users who are unaware or ignorant of the forum rules.
It might help to introduce a mandatory explanation before a user’s down vote is accepted. But that is just going to give a headache to forum moderators and waste the limited resources available for Manager development.