Not sure I see the connection, but happy to listen to the argument.
Taxes are always a disincentive of some kind. Progressive income taxes are a disincentive to increased earnings. Less taxes is less disincentive. Flat tax makes all earners aware, by means of their pocketbooks, the cost of govt. I would be in favor of a flat tax, but that rate can be abused as well if spending is not curbed.
I would also favor a consumption tax replacement to the income tax, but again, that may be abused by large govt.
I’d favor a flat tax as well, but that’s not getting passed by Congress in the foreseeable future.
And, flat taxes in our welfare environment aren’t so flat after all. Most I’ve seen proposed have a hefty exemption to start. EITC and other welfare would warp any flat tax. That’s what Trump’s plan does well: maximizes incentives for lower income people to work.
Also, because it looks like good tax news for so many makes it more likely that his plan would be politically popular, he would get voted in, and the plan would be passed.
Yet, as I pointed out, the most important good to come of it would be the drastically lowered corporate tax rate.