Unfortunately, however, there are many people who have used their religious or secular beliefs to “rationalize”, or attempt to “justify”, unnecessary violence, and often extreme violence, against both innocent human and nonhuman animals.
Religion-Based Violence Inflicted on Innocent Humans
Examples of religion-based violence inflicted on innocent humans include the notorious Inquisitions from about the 1200s to the 1700s, which authorized torture in investigating heresy and execution by live burning of convicted heretics; related witch burnings in the 1500s and 1600s; religious colonialism; religious wars of all kinds; and religious and biblical “justifications” of human chattel slavery.
When we look at religion-based violence against humans, we see that it is usually  not the religious beliefs per se, but aggressive people and groups violently forcing the religious beliefs on others that are the problem.
Secular-Based Violence Inflicted on Innocent Humans
Examples of secular-based violence inflicted on innocent humans include violent uprisings in support of political ideologies from the far right (fascism and Nazism) and the far left (Soviet and Maoist Communism); violent uprisings in support of liberalism (secular and economic colonialism against indigenous people); human chattel slavery in agriculture-based economies; and morally questionable wars fought for mostly economic interests, rather than for legitimate national defense, per se.
Again, as with religion-based violence, when we look at secular-based violence against humans, we see that it is usually  not political ideologies per se, but aggressive people and groups violently forcing the ideologies on others that are the problem.
Religion-Based Violence Inflicted on Innocent Nonhumans
Examples of religion-based violence against innocent nonhumans are manifested in people’s consumption of lactation products, eggs, and flesh; use of leather, wool, and fur; attendance at rodeos, zoos, and circuses; and support of animal experimentation, etc. The idea is often stated that God “put” nonhuman animals here “for us” (which is remarkably similar to the religious justification of human chattel slavery). Another idea is that God granted rights to humans, but not nonhumans (or white humans in slavery days, but not nonwhite humans in slavery days), so that we are justified in inflicting unnecessary and intentional violence on them in the form of slavery, exploitation, punishment, and death.
If we give this notion that God has sanctioned unnecessary violence toward the innocent any thought at all, we see that the religious beliefs themselves become ludicrous. The notorious “Problem of Evil” in justifying a morally decent god’s existence in light of evil so ubiquitous in the world becomes absolutely insurmountable. After all, any god who intentionally created innocent, sentient beings for the purpose of food, clothing, entertainment, or experimentation is certainly a monster worthy of the strongest contempt. We may fear such a monster dreadfully, but it is insane to worship such a morally repulsive entity. Obviously, the same goes for any god who would sanction torture and live burnings. We might fear such a nasty, powerful entity, but we cannot coherently worship one. On the other hand, if a god desires nonviolence toward all sentient beings as manifested in veganism, only then is the god good and worth worshiping. To believers I ask, “Which is it? Is God good or monstrous?”
Secular-Based Violence Inflicted on Innocent Nonhumans
Examples of secular-based violence inflicted on innocent nonhumans are again manifested in people’s consumption of lactation products, eggs, and flesh; use of leather, wool, and fur; attendance at rodeos, zoos, and circuses; and support of animal experimentation, etc. Secular speciesists generally use Darwinism and Hobbesian social contract theory as their “justification” for inflicting unnecessary, intentional violence, killing, and harm on the innocent.
They claim superiority over other species on the basis of their supposed “rationality”, “empathy”, and ability to enter into an imaginary “social contract” with those people whom they presumably would otherwise exploit, harm, or kill (good thing for that imaginary “contract”); but in a spectacle of self-contradiction, adjust themselves to the level of supposedly “non-rational, non-empathic, amoral” animals in exploiting, harming, and killing other species. One might think I was referring to people who lack self-control and emotional development in describing such irrationality, but no, I’m talking about supposedly emotionally mature human adults with fully-developed prefrontal cortexes. It boggles the mind how strongly irrational cultural prejudice and, in some cases, social pressure, can completely dominate otherwise intelligent, independently-minded people. For a brief analysis of such irrationality, see my essay entitled “Rational Ignorance and Rational Irrationality”.
Stop the Unjustified Violence
There are no excuses for unnecessary violence, exploitation, harm, or killing inflicted on innocent human or nonhuman animals. All of the “justifications” rooted in various religious and secular beliefs are really a reflection of the nature and cumulative environment of the individuals who espouse violence. But many individuals can, to a large extent, overcome their past environment by willingly committing themselves to nonviolence and nonviolent environments.
Veganism, by definition, is the rejection of unnecessary, intentionally-inflicted violence, harm, exploitation, or killing regardless of the species membership of the innocent sentient being who would be the victim of such violence. If you are not a vegan, learn how to go vegan starting today (see some of the links in the sidebar for information about how to go vegan). If you are a vegan, encourage others to go vegan by informing them on why and how.
 The exception to the religious beliefs themselves being violent or harmful is that of specific chapters and verses in holy books that promote violence (whether it be killing, slavery, rape, war, torture, or any other form of violence).
 The exception to the political ideologies themselves being violent or harmful are doctrines of violent revolution in some left-wing ideologies, and implied or expressed social Darwinism, and greed, and self-absorption lurking behind many right-wing ideologies.