A sociopath is someone without a conscience. That's the dictionary definition, and it's absolutely applicable in this case.
"The term sociopath is used by the public at large" Sociopath is a word, but not a diagnosis.
"and is pretty much always used"
"to dismiss the possibility of empathizing"
"with someone you don't understand or don't agree with."
In this example, you are saying he has no conscience whatsoever. This excuses you from trying to understand who he his, it excuses you from asking a question like, "What values and circumstances led him to make this decision?" You want to believe that no possible set of reasonable values, under any circumstances, could ever lead a man to make these decisions. He must have no values. He must be a "sociopath". A good, normal person like yourself could never make decisions like this. He must not be a good, normal person. He must be something else, he must be "a sociopath". He must be some special label that allows you to put him in a box where you don't have to empathize with him, where you don't have to try to understand who he really is or why he made these decisions.
His actions were without conscience, therefore he has exhibited sufficient traits for society to treat him as a sociopath. Such social cues are a major part of how humans interact, and your lack of awareness of them probably means your time would be better spent reading up on autism instead of psychopathy.