What about this verse? "I will cast terror into the hearts of those who disbelieve. Therefore strike off their heads and strike off every fingertip of them."~Quran 8:12
How exactly is hacking the heads of of people who don't believe the same thing you do an example of "self defense?"
Please read the previous verses
When you were calling upon your Lord for succour, and He answered you, I shall reinforce you with a thousand angels riding behind you. (8:9)
So God sent 1000 angels to fight with the believers, actually at those time the disbelievers were great in number and power.
God ordered the angels to fear the disbelievers and to support the believers as shown in next verses.
God wrought this not, save as good tidings and that your hearts thereby might be at rest; help comes only from God; surely God is All-mighty, All-wise. (8:10)
When thy Lord was revealing
to the angels, I am with you; so confirm the believers. I shall cast into the unbelievers hearts terror; so smite above the necks, and smite every finger of them! (8:12)
You did not slay them, but God slew them; and when thou threwest, it was not thyself that threw, but God threw, and that He might confer on the believers a fair benefit; surely God is All-hearing, All-knowing. (8:17)