Who needs it? Well, we do things with that tax money. Fight wars, build roads, pay for health care. Needs? Seems like the wrong word and the wrong frame you're trying to set up.
We have a deficit, and we still have wars to fight and bills to pay. So, like any family, we ahve to come together and seeks spending to cut and revenue to increase. This is rather basic.
Jobs or employment is a bit of a different issue, but the evidence is rather clear, tax cuts don't create jobs.
As for the 80's, did you look at the increase in military spending? Now that's a third reason you can add to the other two I gave you. Have you considered looking up the history of the 80's?
Again, we see inconclusive evidence for the power of tax cuts. We do see small peaks in median income growth, a good measure of how the average American household is doing, after top-bracket tax cuts in the mid-1960s and early 1980s, but we also actually see income decreases after the tax cuts of the late 1980s, and strong growth after the tax increase of 1993. It is true that in the year with the worst median income decrease (3.3% in 1974), the top tax rate was 70%. However, it was also 70% in the year with the highest median income growth (4.7% in 1972)! Once again, the lack of connection between the two measures is backed up by a correlation coefficient near zero: 0.06, to be exact. And yes, yet again, the coefficient is positive, indicating that income has gone up slightly (though negligibly) more in years with higher taxes.
Trickle-Down Economics: Four Reasons Why It Just Doesn't Work | United for a Fair Economy
If you follow budget debates carefully, you will sometimes hear the same politician, in effect, making opposing arguments. When arguing in favor of tax (rate) cuts, a politician may make the supply-side claim that government revenues will increase as a result. When arguing against new or expanded government programs, however, they may argue that the new spending will require tax (rate) increases.
If they really believe the supply-side story, they should be arguing that increased government programs will require tax cuts, in order to increase tax revenues.
EconoFAQs: Do Lower Tax Rates Really Increase Government Revenue? | Dollars & Sense