No wonder the WWII generation was labeled the "Great Generation." People today, represented by posters like yourself, too frequently conclude, "Nope. Can't handle multi-tasking. One foe at a time, thank you."
Higgmeister, just face it: A LOT of conservatives take their cultural cues from people like Jesus Christ and the apostle Paul.
Here's Jesus:
"I tell you, my friends, do not be afraid of those who kill the body and after that can do no more. But I will show you whom you should fear: Fear him who, after the killing of the body, has power to throw you into hell. Yes, I tell you, fear him." (Luke 12:4-5)
So does Jesus say, "worry about the 'greater evil of Islam?' (Nope)
Instead, does He say to exercise fear of the One who has authority to cast somebody into hell? (Yes)
So, indeed, our "fear" is on behalf of those who are placing their eternal spiritual lives at risk.
As for "uniting" vs. this 'greater evil," I could probably guess that the folks who the apostle Paul warned the church @ Ephesus about had the bulk in common with the sheep there. Both groups were "religious." So, did Paul play the "allies"-game-don't-divide-us-some posters play? (No)
As Paul was leaving the church of Ephesus, he warned them with this high-priority alert:
"I know that after I leave, savage wolves will come in among you and will not spare the flock. Even from your own number men will arise and distort the truth in order to draw away disciples after them. So be on your guard! Remember that for three years I never stopped warning each of you night and day with tears." (Acts 20:29-31)
Paul's cultural priority? (Defend against the false disciples who will proselytize the flock and draw away men unto themselves!)
Tell us something, higgmeister: If you did something tearfully night and day for three years, do you think it's rather important? So what? We're just to conclude, "Oh, the man who contributed a good chunk to the New Testament -- what does he know about cultural priorities?"
You have an opportunity to proselytize and convert Mormons that you will never have with Islam.
All of the above sets a priority for us all.