"Good And Evil are unquanifiable abstracts. What should they matter to me?"
The same is due to God. There is no irrefutable evidence of a God or Gods existing, having existed or never having existed. -Lehah
1) Agreed: that God is unquantifiable, and to most human minds, too abstract.
2) Likewise agreed that good & evil are unquantifiable (that is, not fully quantifiable), and often maddeningly abstract.
But most folks would disagree that they "shouldn't" matter to us, either as a society or as individuals. All government (even the most corrupt ones) is based on the idea that there are certain things that are "good" for the society, and there are other things that are bad or "evil" for the society. This has a way of making it into the laws & codes of that government. This goes down even to the level of every sentient human who's ever walked the planet. If you have anyone in this world you love (even if that person is yourself), you no doubt seek to do good for that person when you can, and seek to avoid having "evil" happen to that person. Even the most depraved, amoral, sociopath criminals live this out in their own lives.
How? By seeking, when they've done their latest crime, to avoid capture/punishment; Whatever little conscience they may have knows they've done "evil", and seeks the greatest "good" for themselves (i.e., to avoid the pain of having to pay the price for their deeds).