The argumentum ad imperfectionem is a kind of fallacious argument advanced by lazy meta commentators.  It consists in alleging that the imperfections in the arguments of certain peripheral exponents of a particular view justify the weak-manning of the opponents of those views.   

So for instance, some less than responsible or scientifically accurate characterizations of the family of views known as climate change justify the wildly erroneous allegations of global warming deniers.  Here's an example from the Washington Post's Dana Milbank:

As a scientific proposition, claiming that heavy snow in the mid-Atlantic debunks global warming theory is about as valid as claiming that the existence of John Edwards debunks the theory of evolution. In fact, warming theory suggests that you'd see trends toward heavier snows, because warmer air carries more moisture. This latest snowfall, though, is more likely the result of a strong El Niño cycle that has parked the jet stream right over the mid-Atlantic states.

Still, there's some rough justice in the conservatives' cheap shots. In Washington's blizzards, the greens were hoist by their own petard.

For years, climate-change activists have argued by anecdote to make their case. Gore, in his famous slide shows, ties human-caused global warming to increasing hurricanes, tornadoes, floods, drought and the spread of mosquitoes, pine beetles and disease. It's not that Gore is wrong about these things. The problem is that his storm stories have conditioned people to expect an endless worldwide heat wave, when in fact the changes so far are subtle. 

Other environmentalists have undermined the cause with claims bordering on the outlandish; they've blamed global warming for shrinking sheep in Scotland, more shark and cougar attacks, genetic changes in squirrels, an increase in kidney stones and even the crash of Air France Flight 447. When climate activists make the dubious claim, as a Canadian environmental group did, that global warming is to blame for the lack of snow at the Winter Olympics in Vancouver, then they invite similarly specious conclusions about Washington's snow — such as the Virginia GOP ad urging people to call two Democratic congressmen "and tell them how much global warming you get this weekend."

That's just nuts.  Gore and the climate change activists are correct (Milbank doesn't doubt that), but examples used in their arguments may give lazy or just plain dishonest people the wrong idea.  It's their fault, in other words, that they have used anecdotes to illustrate claims about the consequences of a warming atmosphere.  Giving examples, anecdotes in other words, is one way a view can be communicated.  These anecdotes, by the way, are not perfect.  They are not perfect especially in the hands of people with no particular scientific training or real grip of the view they hold.  A view, in this circumstance, which turns out to have a sound justification. 

Misrepresenting the scale or significance of the imperfect anecdote in order to undermine the view is what we call "weak manning," that is, distorting a view by selection of its weakest justifications.  There likely are lots of these.  But this does not justify the dishonesty of people who know of better arguments.  And the existence of weak exponents of a particular view does not entail that the view itself is weakened.