At some point in the reasoning chain you reach the bad thing that is bad because its intrinsically bad and if you try to reason more you'll just go in circles. Or you enter a philosophical debate of such depth that it's stupid to have it with internet strangers.
Drink driving is bad.
Why is that?
You might cause a crash.
Why is that bad?
People could die.
Why is that bad?
They'll be dead.
Why is that bad.
They don't get to exist any more.
Articulate your reasoning!!!!