The CBO does not understand economics; they are accountant number crunchers. When people are allowed to keep more of their wealth regardless of mechanism, there is more capital available for investment. Closing loopholes is not going to have a "positive impact on the supply of labor." It is ridiculous to claim otherwise.
I would not be against closing loopholes if ALL rates were reduced, but absent reduction in rates for EVERYBODY, closing loopholes is raising taxes, and that is immoral. The amount of revenue gained from closing loopholes + reducing rates should be zero or close to it. Read my lips: Any other number means you are raising taxes.