Just the obvious evidence. America is 75 per cent Christian, or 225 million folks out of about 300 million total population. America is in serious trouble in many crucial areas. These problems are caused by the citizenry at large, which as noted is 75 per cent Christian. I believe that if Christians were better citizens our national problems would diminish greatly. Regarding Muslim citizenship; the problems found generally throughout Christian America are almost absent in the Muslim community. This not to say that all Muslims everywhere are good citizens, but the vast majority of those living in America are very good American citizens.
1) You're talking about people who claim the faith when polled, but according to Barna, only a fraction of the 85% of Americans who claim to be Christians could rightly be called adherents. If somebody's a non-adherent, then Christian reasoning for said person to be a better citizen or a better person will fall on deaf ears.
2) You haven't defined what a "good citizen" is or does. But if it's what I was raised to believe what a "good citizen" is and does, most of the "good citizens" in this country must be, by the numbers, at least nominally Christian.
3) I have not seen a contrast between the behavior of Muslims and Christians myself. I grew up with a couple Muslim guys in my grade. They didn't eat pork, and their dad made them get up for prayers, but they cursed, drank, made coarse jokes, broke the speed limit (including one glorious incident where one was doing 62 in a 25 zone) and generally lived no better or worse than the rest of us. Now, they weren't really "in community" in the sense that one would think of an Amish community or a Jewish community, so your mileage may vary. But from what I've read about Muslim countries, and from what I hear about Muslim exchange students who come here, the youth are hard partiers over there, too. But of course over there, being a "good citizen" will be different, since most of those places are police states. And in those countries, I have no reason to believe that where Christian ethics and Muslim ethics intersect, that the Christians are any worse citizens in their own countries than the Muslims.
4) Concerning the Muslims over here who are good citizens (that means the Nation of Islam, other separatist movements, and mosques tied to international terrorist groups are all out) you're dealing with a much smaller pool of people who have something to prove. Over the last 9 years, they've known that all eyes are on them, so what I've found is they'll generally go out of their way to be nice.
5) We must also consider that first-generation Muslim immigrants generally come from less permissive cultures. This does not contradict my third point; some sins are far less tolerated than others. It might be one thing to have a drink, but Heaven help you if you're a teenage girl and you decide you want to marry someone other than the man Daddy picked for you. When you come from a culture with strict punishments for certain deeds, you'll be that much less likely to do whatever deeds bring those punishments. It takes at least one generation, and in some cases more, for these norms to relax a bit more in families, as they integrate with the culture around them.
6) You also need to tell us what "problems" are "caused" by the citizenry. Is the citizenry causing the massive deficits and inflation of the currency, or are politicians doing that? And one must also consider what laws politicians pass which steer the citizenry to act in destructive ways. Lastly, our government is good and clean compared to the governments of all Muslim countries. Whatever this says about Islam, the comparison is not favorable.