This is in response to the rec-listed diary today.
The laundry list of errors and misconceptions quoted in the above-linked diary is staggering both in its size and stupidity. But -- and here comes the dreaded "but" -- there's a small grain of truth in it.
Yes, a muslim can be a good American. However, to some extent being a good american requires a muslim to be a bad muslim. To put it bluntly, Islam is not well-suited to secularism. Its holy books promote both evangelism (like Bible, but unlike Tanakh) and theocracy (like Tanakh but unlike Bible). Together, the mixture is not a good fit for a secular state.
The obvious caveat is of course in effect: it all depends on how religion is practices de facto, not on what is written in its holy books. However, the content of the holy books does matter, as it frames and channels and restrains the possible expressions of the actual theology and practice of specific forms of a given religion.
Secularism being understood as essentially the separation of church and state, scripturally Christianity lends itself to secularism fairly easily ("give ceasar's to ceasar" etc.) Judaism does too, outside of the actual jewish state (as anyone who lived in Israel, like I did, can tell you, the religious fundies there are pretty scary politically, and they are thoroughly theocratic, except for the ones which think modern Israel theologically illegitimate in the first place). In Israel you see all the time the secular and religious values in open and indefatigable conflict, but outside Israel, Judaism poses no theocratic threat. Judaism being non-evangelic, outside of Israeli zionist fundamentalists (as opposed to those anti-zionist fundamentalists who think modern Israel is theologically a mistake) it's arguably the most benign abrahamic religion.
However, scripturally Islam neither recognizes the separation of church and state (unlike Christianity) nor, while essentially embracing theocracy, restricts its evangelic fervor (unlike Judaism). As such, in Islam we do in fact get a theological, scriptural drive to both evangelize -- and to establish theocracy in muslim lands.
Of course there are plenty of muslims which essentially ignore that, Turkey and Indonesia being prime examples of countries populated by such. However, in foregoing quranic evangelical/theocratic aspirations, those muslims are in fact violating the scriptural precepts of their faith in a way that neither christians nor jews must.
Along similar lines, christians for example violate the scriptural precepts of their faith all the time -- both in the direction of bigotry and destruction (onward christian soldiers!) and in the direction of kindness and tolerance (eschewal of the old-testament brutality for example). However, those precepts still remain, and still loom over various christian denominations.
There are of course muslim denominations which eschew the evangelical/theocratic aspirations, but in doing so they twist themselves in pretzels to explain away Quran's call for evangelizing (by word or by sword) and subsequent theocracy. Similarly, there are christian and judaic denominations which are genuinely welcoming to gays, but they attain such attitudes despite their religious scriptures. They swim against the tide.
So to answer the titular question once more -- can muslims be good Americans? -- the answer is YES; but to the extent to which they accept our secular state and our constitutional system of governance, they must sacrifice their scriptural fidelity. The same applies, for example, to genuinely homosexuality-tolerant christians and jews: to the extent to which they eschew homophobia (not merely support equal rights for gays, but actually reject condemnation of homosexuality on both theological and personal level), they go against the Old Testament.
We can fully recognize that muslims can, and are, good americans -- and yet also recognize that in becoming such, they must struggle against the scriptural precepts of their religion. This is, unfortunately, a common trait among beliefs born in the more brutal times.