Here it is people, the answer.
(The question, by the way, is: politics – why?)
The answer is:
Hume’s Guillotine’: One of the core philosophical problems of all time. That is ‘‘can an ought-statement (we ought to do …) be entailed by an is-statement or set of is-statements (the situations is …)?’
What this means is that just because we can describe reality doesn’t mean that we can logically derive an ought-statement from that description.
So we can marshal as much evidence as we can to argue our cases but at the end of the day what we are really arguing over is our values and beliefs.
I believe these are right but they can never be proven absolutely. Hence politics.