If you want to go to extremes you could claim it as being in the interests of national security. By stopping him suffer heart problems later on you're saving the nhs money, which saves the government money, which can be spent providing the military with the correct equipment for the conflicts they're in.
The preemptive self defence is valid though. So long as you can legitimately claim that the other person's actions lead you to believe you were about to be assaulted if you didn't take action, then you're entitled to take action. If someone is pissed up and being aggressive towards you it's reasonable to think that they could be about to hit you, so you're allowed to prevent them so long as the force used to do so isn't excessive.
