"I don’t know the best way to defeat ISIS. Neither do you. I don’t know the best way to negotiate trade policies. Neither do you."
The first plank of the argument is that he can't make a call on most issues and so he's not qualified to weigh in. Welcome to democracy. The job is to make the best choice that you can with imperfect information. If you can't do that then do the rest of us a favor and abstain.
"You can argue whether an estate tax is fair or unfair, but fairness is an argument for idiots and children."
The second plank is that he might be less well off if the estate law changes.
So now the lack of an opinion on any other issue makes sense. If you had to think about ISIS or trade (or walls or Muslims or women) then maybe a dent in your income would have to move down a position or two or fifty. But if, aw shucks, you're just not smart enough to make those calls then it's a conveniently self-serving single issue election.
All of this is true even if raising the estate tax is a bad policy. But at the risk of coming across as a child or idiot maybe there's something in it:
"Between 1979 and 2007, paycheck income of the top 1 percent of U.S. earners exploded by over 256 percent. Meanwhile, the bottom 90 percent of earners have seen little change in their average income, with just a 16.7 percent increase from 1979 to 2014."
I don't know the best estate tax policy. But Scott, neither do you.
Updated 2016-10-12 20:28:
So over the weekend he switched his endorsement to Gary Johnson. Maybe:
"You might enjoy my book because you’re not sure if I’m really endorsing Gary Johnson or just saying so to protect my brand."