This is a false equivalence because the government and the private sector spend money on very different things. If the tax cuts end up being funded by reductions in entitlement spending, for example, the private sector won't funnel money into Social Security and Medicare to offset those reductions.
>If the Republicans are right, they'll spur enough economic growth to be a net gain across the board in both new economic activity (wealth)
CBO projections imply that the nearly all of the long-term gains from the tax cuts will flow to foreign investors [0], so it certainly won't be a net gain for the US as a whole.
[0] https://www.brookings.edu/blog/up-front/2018/05/10/cbo-estim...
Voodoo Economics