Your objection assumes that said terrorists would be wearing Islamic garb, sporting beards, and publicly bowing east for prayer. We just heard about Khalid Sheikh Muhammad's plans to employ southeast Asian Muslims for a follow-up to 9/11. So, who exactly will we be profiling? Anyone who isn't white? So they'll use Chechen/Baltic types.
Anyone carrying a suitcase nuke would assumedly vaporize with everything else, anyhow, so we probably wouldn't even know the ethnicity of said nuclear bomber.
It would get nasty is all I am saying and populus would become involved.