It's not a huge drain of resources. The new Joint Strike Fighter program and various other R&D projects that don't work and aren't needed are huge drains of resources. But yes, we know the reasons for why many of these people are leaving their home countries to join ISIS. They tend to have the same profiles, similar backgrounds, etc. We need to seriously start addressing these reasons, otherwise we'll never solve this problem using only military tactics.
What if they didn't kill anyone? Maybe they never even saw combat. You said all returning fighters should be tried for "murder, terrorism and treason." I'm saying that some of those who go to join ISIL come to regret their decision, and the main thing keeping them from returning is fear of being tried for treason. In some cases, there's a benefit to bringing some of these guys back that outweighs the potential risk of harm and your need to see them put in prison for life. If not, then yes, they're probably screwed.
