Why do people have such a hard time with God ordering...?

women, children, and babies to be slaughtered in the OT? First of all, the men were very bad men and that alone should warrant the destruction of their families. Second of all, kids can be such a handfull. God could not find any rigteous people to watch over them and even if he could have why spare them for they were just going to grow up to become evil like their fathers. Even though it states in the OT thou shall not kill God likes to change the rules a bit here and there. Maby he should have said "Thou shall not kill unless they are killing evil men and in that case they shall slaugter their entire families as well." I just dont understand how people cannot believe that a loving God could order his followers to commit genocide and tortures people in hell throughout eternity for not being aware of the one true religion out of thousands of them even though God has never given us direct proof of his existence.