British ISIS fighters must be killed

The notion of a right to fair trial has existed since at least 1948 when it was ratified in the UDHR. Political correctness originated around the 1990s/2000s.

A trial is used to determine whether someone is guilty. Even if you wanted to kill terrorists you'd need to put them to trial before you can even convict them of wrongdoing. Otherwise you're opening up a bag of worms where "well, we think he is a terrorist" is the norm and you can quickly justify anyone being killed; there would be no trial hence no evidence to the contrary is needed.

What threat are British ISIS militants if they are outside of the country? They're probably hungry in some ravaged Syrian city facing constant attack from Syrian and Iraqi forces, as well as airstrikes from God knows where.

Actually no, we don’t put terrorists on trial before we kill them. Bin Laden was not put on trial, nor were many terrorist militants killed in drone and air strikes. The notion that we should put 600+ British terrorists on trial is absurd and logistically impossible to pull off when you take into account that for trials to happen capture must occur first. Right to fair trial is a civilian concept which does not apply to enemies of the state. British ISIS fighters are a threat because if they make their way back to mainland under the radar of the authorities they will carry out attacks. Recent incidents in Europe has demonstrated this to be true. The government should authorise a merciless crackdown on every single Brit traitor who went to fight with those swine.

Why is this a good thing?

Terrorists, at least in this context, fight against western values. The right to a fair trial is a western value and for at least half a century. You're giving them a system they want by disregarding human rights.

What recent terrorist attacks in Europe have been committed by British ISIS fighters who have returned?

The right to fair trial applies to civilians who are suspected of committing civilian crimes, like theft or fraud. It does not apply to enemy combatants. By your absurd logic, we would have had to put every single Taliban fighter in Afghanistan on trial before we killed them. Wars would become unwinnable. We are at war with ISIS. We're not giving them anything but a fast-track to the martyrdom they crave so badly and would kill us for. F*** their human rights, they disregard the human rights of others all the time. It is an infinitely safer option to treat British ISIS fighters as enemy combatants and hunt them down via drones or air-strikes on Syrian and Iraqi soil before they return to the UK.

Not British ISIS fighters, but returning ISIS fighters from other European countries.