I'm writing this because Mira told me to. And it's always wise to agree with Mira. Something terrible and hilarious will happen otherwise. And we can't have that.
So... what do you do when you have opposite critical advice from your readers? One critter (devil) says "You have to cut this whole section", and one critter (angel) says "You have to expand this whole section." It's not an entirely uncommon experience if you're in a critique group, and there's a tendency for the writer to react with paralysis. What to do? How to choose? I think the common wisdom (Stephen King, for one, seems to espouse this in On Writing) is that you do nothing. The house (writer) wins. In this little game of critical blackjack, the first option is to do nothing, as opposite views cancel each other out.
This is safe and easy, I guess, but not necessarily correct. Two people have latched on to the same element and commented on it - and not because it was working. Just because their solutions (being contradictory) may not be right, it does not erase the fact that there might be an underlying problem.
I think one of the difficulties is that writers want to group the critiques together. They want a consensus, as simple patterns are easy to interpret. So we group the crit comments together, whether it be two, three or four comments on a particular element. I don't feel this is the best approach, however, as it can be misleading. Each comment is its own and separate thing, and should be considered as such. The crit's not important... it's what you do with it. The best crit in the world is useless if you can't apply it and make your story better.
Each comment deserves to be evaluated separately. You have to take time and think, balancing the comment against your own internal vision of the story, of what you want it to accomplish. Evaluate the comment with your own aims in mind, rather than merely looking for crit consensus.
Even complete agreement within your critters can be misleading. If they all trip on the same thing, yes, there likely is a problem. But if they all suggest a cliched solution? Do you take it because there's consensus? It comes down to understanding. Try to understand the comments... and try to understand your story, what you want from it. Try to understand how you can achieve the effect you want. If A and B offer opposing comments, you may find that you want to take A's view, or maybe B's, or maybe a combination of A and B. Or maybe do as King suggests and do C (nothing). Or maybe the right answer is D, something you thought of all on your own, something that approaches the root problem rather than the surface ones.
The true advantage of getting critiques is not the advice you receive, but the opportunity to see your story in a new way, with new eyes. It allows you to step out of yourself and become the reader for a moment, and this in turn allows you to shape the words of the story to more closely achieve the effect you want. Yeah, we're manipulative. That's the job. To create something that is not there, an illusion that the reader willingly adopts - if you're convincing enough, if your manipulations are deft enough. And critiques can help us perfect that manipulation, each in their own turn.