Elite097
I am not sure but isn't D a strengthener here because we are saying that policies could be detrimental to the functioning of govt (probably because they cannot get compromise); so they must not be honest about it all the more because if they are detrimental and they are being honest about it, then definitely they will not get the necessary compromise.
Also I am bad with politics and I do not understand how this is working- which compromise is being referred to? Who will compromise with whom? How will any compromise be beneficial to anyone? How will being honest/ dishonest about it lead to any compromise? Why does member of A political party have to express honest opinions about them?
MartyTargetTestPrep GMATNinja KarishmaB ThatDudeKnows avigutmanConclusion: insincerity shows gov't functioning well
Premise: honesty would make compromising difficult
So, insincerity-->compromise-->gov't functioning well
Answer choice A does a good job of breaking that last arrow, so I hope you're comfortable that A is the right answer.
Okay, now for your questions.
First, a disclaimer: I can't caution you enough about spending too much time in the rabbit hole that is "what if the question asked __." Trying to figure out whether an answer choice on a weaken question would qualify as a credited response if we were instead asked to strengthen is a variation of that. People love to do this analysis, and I think it usually just distracts from the REAL take-aways from a question. My suggestion is never to do it.
That said, here's a little discussion on D.

If you need to go through as many steps in a logical progression as you did in your explanation (and especially if your explanation includes the word "probably"), I can all but assure you that you've got the wrong answer choice. GMAC asks us to follow logical progressions, but keep in mind that with each step along the path (unless the steps are rock solid), the path gets a little shakier. Too many steps ends up with a very shaky path, and that's not what GMAC is after.
I don't agree with your path on D. If a policy is detrimental but I'm able to get it enacted by compromising with you, such that you support my detrimental policy in exchange for me supporting whatever it is that you want, then my detrimental policy won't result in the government functioning well, and government functioning well was our conclusion. But just because some policies could be detrimental, that doesn't show that government isn't functioning well. Maybe the detrimental policies won't get enacted for some other reason aside from the honesty/insincerity bit. As above, though, I'd get out of this rabbit hole and move on to a different question!
As for politics, generally, perhaps the second sentence of the preceding paragraph helps clarify how GMAC was using the concept of compromise in politics?