I agree that a tax cut can be good if "it means higher family income". A good tax cut would do this by either lowering lower and middle-class taxes or by incentivising businesses to hire middle-class workers and pay them good wages. This would lead to increased consumer spending and improve the overall economy.
A bad tax cut lets businesses and the rich keep more of their money to themselves. They are then likely to invest it in things such as rental properties and financial companies, which tend to drain money from the lower and middle classes. This leads to decreased consumer spending and worsens the overall economy.
The Trump tax cut is a bit of a mixed bag, but the good part is scheduled to disappear, and the bad part isn't.
This also ignores the national debt, which
was decreasing as a percentage of GDP in the '60s, but is much higher and increasing now.