Every cause spawns them. Whether it's a political party, an interest group, or a religious sect, a few adherents will inevitably feel called to militant defense of the group's beliefs and interests, or aggressive proselytization. And without exception, zealots feel vindicated by persecution.
Christian religious types look to the Bible for their commission to suffer for the cause:
Only conduct yourselves in a manner worthy of the gospel of Christ, so that whether I come and see you or remain absent, I will hear of you that you are standing firm in one spirit, with one mind striving together for the faith of the gospel; in no way alarmed by your opponents--which is a sign of destruction for them, but of salvation for you, and that too, from God. For to you it has been granted for Christ's sake, not only to believe in Him, but also to suffer for His sake.Of course, every religion points to their own Holy Writ for similar instruction to suffer as part of the whole "zealot" thing. The problem is, not all suffering is created equally; some religious zealots aspire to suffer in hope of heavenly rewards, while others accept suffering as the natural consequence of refusing to participate in a world system they feel is irredeemably corrupt. The Bible hints at a way of discerning the difference:
(Philipians 1:27-29 NASB)
For the word of God is living and active and sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart. And there is no creature hidden from His sight, but all things are open and laid bare to the eyes of Him with whom we have to do.God gave us His word so those who wish to follow in His Way might discern their inner motives and stay on the path proscribed for them. Faithfulness is its own reward, and those who hope for a more tangible perks, such as a badge of courage or heavenly bliss will, in the fullness of time, be sorely disappointed.
(Hebrews 4:12-13 NASB)