that line was the Laffer Curve, and it was talking about when taxes became counter productive - on the high side.
My biggest problem with the Trump Plan is that 50% pay no income tax. I’m not sure that’s a good thing. It is gets rid of earned income tax credits, that’s a good thing. Also, the class warfare rhetoric is worrisome.
I don’t distinguish between amounts of money taken from your pay by the government. For those under the SS and MED threshold that is an extra 8% or so from their pay going to the government. We have known for forever that it goes into the same pot. The so-called 47% pay that tax. It might be decades if ever before it’s their turn to get it back. The impact on their household in the here and now is that it is a tax.