I know this is an extreme case, and tough cases can make the law challenging, but it's mind-boggling that anyone would want to declare this person an enemy combatant.
Essentially, you're saying if a member of the FBI wants to, you can be held for an indefinite amount of time without a trial or due process or the opportunity to contact anyone. Period.
It would literally allow any member of the FBI to legally kidnap any American citizen. A federal agent could detain his ex-girlfriend's new boyfriend because he thinks he's a ####.
You might think "well this case is different, this guy is a terrorist." Well, what makes him a terrorist? The FBI thinks he's a terrorist. Are they right? In this case, yes. But the FBI doesn't need anyone to rubber stamp the decision to label him a terrorist to label him an enemy combatant and ignore due process.
Now if you have a ton of faith in the FBI's discretion, this isn't an issue. If you think the federal government needs to have its power checked -- which, I thought, was the core principle of every conservative movement -- then the idea that a US citizen could ever be labeled as an enemy combatant and held without any due process should be considered repugnant.