But why do they believe those?Because they like their good lives and those beliefs support their nice way of lives.Threaten to ruin their lives and then see if they are still remain that nice.
Defending oneself, others, and even imposing order on the unruly are not necessarily inconsistent. In the "do unto others" vein, I personally expect that if I violate the agreed-upon rules of society, then I should expect consequences for my actions to be imposed by the other members of the society of which I am a part. But I also expect that I myself, and everyone else in society, will have pretty much freedom to decide and pursue what is our own idea of the good life--as long as it doesn't interfere with others' attempts.
I also expect people not to fight with each other, and if they do, to expect others to defend themselves, others, and society as a whole.
Yes, I like my good life; I am willing to fight and die if necessary to defend my good life; I'm even willing to have rules in society to discourage those who would disrupt society and people's chosen good lives because "we are the enemy" of someone else.