iconoclast

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who attacks and seeks to overthrow traditional or popular ideas or institutions.
• noun One who destroys sacred religious images.

from The Century Dictionary.

• noun A breaker or destroyer of images; a person conspicuously hostile to the use of images in Christian worship.
• noun One of those Protestants of the Netherlands who, during the reign of Philip II., riotously destroyed the images in many of the Roman Catholic churches.
• noun Hence Any destroyer, denouncer, or exposer of errors or impostures; one who systematically attacks cherished beliefs.

from the GNU version of the Collaborative International Dictionary of English.

• noun A breaker or destroyer of images or idols; a determined enemy of idol worship.
• noun One who exposes or destroys impositions or shams; one who attacks cherished beliefs; a radical.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One who destroys religious images or icons, especially an opponent of the Orthodox Church in the 8th and 9th centuries, or a Puritan during the European Reformation.
• noun One who opposes orthodoxy and religion; one who adheres to the doctrine of iconoclasm.
• noun One who attacks cherished beliefs.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a destroyer of images used in religious worship
• noun someone who attacks cherished ideas or traditional institutions