So who picks which genocide to go to war over?
Here in the US, the President is our Commander in Chief and has full control over our armed forces outside of the United States. Their use of this power is checked by the US Congress who can make declarations of war.
Other countries have different decision making process'.
Which country is responsible to send their sons and daughters to die?
Whichever country is willing to stand up against genocide. For example, those currently in the coalition against ISIS include Saudi Arabia, the UAE, Turkey, Jordan, Egypt, Qatar, Iraq, Barbarian, the United Kingdom, Australia, France, Germany, Canada, the United States, and the Netherlands.
Should I send the son or daughter I gave life to?
No, this is not your decision to make. In most countries service is voluntary. And in cases where conscription occurs it is regulated by the state. Not by a persons parents.
All that love and life invested should be ended to do some altruistic bullshit that will continue either way because there is no money to be made in doing it right?
Stopping a rapist will stop the rape. But it will not stop all rapes from ever happening in the future. Likewise, wars end conflicts. They do not end all war.
And altruism is not bullshit. We are a social species. Societies that work together survive. Societies that can't work together don't survive. It is in everyone's best interest to find a way of working together in the sorts of societies that value human life, welfare, and happiness. And sometimes force is a necessary tool to use against individuals who stand opposed to human life, welfare, and happiness.