What Hitler did was legal in his country at the time of the holocaust. So apparently the definition of murder is something more than simply a vote in some cabinet somewhere, that defines what constitutes murder. I believe that murder philosophically is killing of another human being, with what is called "malice aforethought."
"It is murder if a person has killed with ‘malice aforethought’. Contrary to public belief the law does not require an actual intention to kill nor a premeditated plot. A person is guilty of murder if death results from an act intended to cause really serious harm even ifthere was no intention to kill."
above quote from online legal dictionary:
http://legal-dictionary.thefreedictionary.com/homicide
in other words,
killing becomes murder when malice is involved, for selfish gain, or out of jealously, or rage, or any other emotion. Regardless of premeditation or planning, and even if it is not planned. As in an outburst. Police only kill on self defense, either of their person or of another. Military only kills in accordance to the geneva convention policy. And thus would not be considered murder. If a soldier does not follow the geneva convention, they can be tried for murder, and many have.
RE: abortion. Abortion is murder because it involves killing for gain, or other. If a parent is scared and cannot get a job to pay for childs needs, they abort for example. Or if by rape, or by other misdeed. It is still murder, in otherwords, it's not the childs fault that we were raped, or could not get a job. They still merit an honest chance at living a normal life.
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Christian apologist Gregory Koukl wrote that "the assertion is that religion has caused most of the killing and bloodshed in the world. There are people who make accusations and assertions that are empirically false. This is one of them."
[4] Koukl details the number of people killed in various events involving theism and compares them to the much higher tens of millions of people killed under
atheistic communist regimes, in which
militant atheism served as the official doctrine of the state.
[4]
It has been estimated that in less than the past 100 years, governments under the banner of atheistic
communism have caused the death of somewhere between 40,472,000 to 259,432,000 human lives.
[5] Dr. R. J. Rummel, professor emeritus of political science at the University of Hawaii, is the scholar who first coined the term democide (death by government). Dr. R. J. Rummel's mid estimate regarding the loss of life due to communism is that communism caused the death of approximately 110,286,000 people between 1917 and 1987.
[6]" footnotes below...and quotation from online encyclopedia "conservapedia.com"