Is prison not enough? Or death by drone strike? There are few mechanisms in the constitution and common law to revoke citizenship, and most of tjose provisions are on the voluntary relinquishment of one's own citizenship. This proposal is likely unconstitutional, will definitely get challenged at the cost of tens of millions of taxpayer dollars to defend in court. Increased cost, no discernable positive outcome, and ultimatrly no real deterrent effect for the stated targets, who don't give a squat about America at all in the first place. So, no upsude, all downside.