You could care, but really, you're not going to stop them from going... So what's the point in caring....waste of time.
If people, or whatever religious persuasion, are unhappy with all that the UK provides them, and prefer to go to Syria, should we care?
No, you shouldn't as we feel the same way in the U.S. ! It's their right to do what they wish whether we see it as right or wrong. 99% of people are going to do as they wish even if they are misguided.