If we're not going to withdraw then at least Trump can show is disdain for the UN as an organization. Next to leaving the UN Ambassadorship vacant this is the next best way to do it.
I used to think that - but with an outspoken leader like Donald Trump as POTUS, I have come to feel differently.
The UN seems to provide constant opportunities for the United States to make public statements that will be heard throughout the world. Lately those statements have been things the works really needs to hear. Things that set us apart, and show the world that the USA is again the adult in the room..... and that the apology tour is over.
I was never a big fan of Nikki Haley until she became ambassador to the UN. I was often proud of her statements while in that position - the UN is a useless anti American organization and should be kicked out of the USA, and we should reduce our financial contributions to a fraction of what they are - but having an international forum that provides President Trump with another way to voice his leadership has actually been a net plus, IMO.