I disagree completely. Citizens are protected by laws, such as the First Amendment, that are not applied to non-citizens (see the Julian Assange mess for details). If the government can designate a group of people as terrorists, and remove their citizenships for being terrorists, then they can additionally apply yet more tribulations on those people while not straying out of the legal protections afforded to citizens.
You keep saying "ISIS" like it's some magic incantation that makes everything else OK. Try saying "any organisation the government disapproves of" instead, and see how that fits your mental model of what's acceptable. For example:
> you're fighting the wrong things here, if you think that taking citizenship away from any organisation that the government disapproves of is the biggest problem.
I think you'll agree that this would be a big f**ing problem.