Whenever this comes up, I always want to ask people this question.
"Give me an example of a bad Japanese voiced anime?"
If your answer is "There aren't any", then this proves that you're not really judging the acting completely. Because there is no way in the world that it does not exist at all. Part of the judging process also should deal with understanding what is being said as well as how someone is emoting. Look at the original Resident Evil game. It was legendary in how horrible the acting was, but they never sounded bored or uninterested. If this was dubbed in Swahili in the same hammy overacting way, no one who doesn't know Swahili would know the difference.
Another popular argument is that since these were originally done in Japan, that leaving the original voices makes it authentic. That's a great, legitament point. Unfortunately, it falls apart when the anime takes place outside of Japan, but everyone still speaks Japanese. Are you really expecting me to sit there and watch a subtitled show about a Japanese doctor roaming through Germany, but no one he meets speaks German? Or how about the one about the Italian Special Forces fighting Italian terrorists in an Italy where no one speaks Italian? It doesn't make sense, does it? Until you realize that they did it to cater to the projected audience of the region that it was being shown to. So how can you not expect the ones shown in the predominantly English speaking regions of the world to do the same? I do, however, love the fact that "Blood: The Last Vampire" took the real world approach by having Japanese characters speak Japanese, American characters speak English, and the two main characters be bilingual. If you're going to hold on to authenticity as an argument, this is the only type of authenticity that I'll accept.
I look at the original Japanese dub on my anime DVDs as a passing interest after I watched the whole thing in my native language, not as a standard that any deviation will somehow taint no matter how professionally it is done. So I would rather sit through a bad anime dub than have to miss half of what's going on screen to read subtitles. Of course, I would want a great anime dub over either one.