They are twofold. During the Lewinsky scandal, most conservatives and many Republicans made the case that high poll numbers do not mean anything more than, well, high poll numbers. There was this fairly frightening tendency on the part of the press, liberal activists, and the ritzy New Yorker crowd to say that popularity was somehow a defense against any charge. This argument took so many forms and was so prevalent that I think most people didn't even realize they were making it. When discussed in the abstract, the problem with this thinking is obvious to almost everybody.
Popularity is usually morally neutral and is just as often bad as good.
Indeed, in our popular culture bad is more popular than good. The political corollary of this equally obvious. Hitler was very popular. Franco was popular. Mao was popular.