If I come to your country and swear to obey its laws, when in fact I am totally dedicated to destroying you, my oath means nothing.  It is a perjured oath.  If I deceive you into believing my false oath, any legal citizenship that is granted under false pretenses is therefore null and void.

U.S. citizenship is not an irreversible decision.  We rarely take away citizenship, although there may be some cases from the 1950s.  If it becomes necessary to require sharia-believing Muslims to make an open choice between one or the other, the United States would be well within normal legal bounds to withdraw both citizenship and U.S. residency. 

As Newt Gingrich pointed out the other day, Sharia-following Muslims cannot have any national loyalty.  The two are explicitly contradictory.