As long as the mosque is not funded by terorist organsations or actively supporting terrorists they have a right to beleive and practice what they want were they want. Even if they beleive and preach that American culture is rotten and disgusting (somthing they may be right about)and that in an ideal world evreyone would be Muslim. Even if they preach things that evreyone else finds offensive. They still have that right. In a democrocy you have the right say, beleive, and do what you want no matter how offensive it is. That’s what comes along with living in America.
The people who beleive that the mosque is funded by terorists should take their proofs of this to court, if it is found to be true it will not be built.