In theory I agree with you, but this only really holds valid in a world where you cannot get any kind of window into possible future behaviour.  

It's also technically true that we cannot guarantee that a firearm owner will responsibly store ammunition, secure their firearms, and won't use them to shoot up their local school ... but we still ensure every owner has taken a firearms safety course, has agreed in principle to abide by our laws, and has no glaring issues around mental health or social instability. We do what we can to reduce the risk, even though there's really no possibility of eliminating it.

So, if you knew that a certain Salafist sect was virulently against gay marriage, and had a history of persecuting and even killing gays, could you improve the odds of successful integration by screening for membership or participation in that sect? Hard to argue that this wouldn't improve our odds.