This is where supportability comes into play: a short time after the was people understood the need for such measure, today you would have a revolution for such a tax level. In 20 years it will come back, no worries, people will love it.

The top rates were much higher but few people actually paid those high rates due to loopholes.

These days people are paying more in real terms in aggregate.

I’m not sure about that either —- there were no tax havens back then. It’s so much easier since 80s to work around the tax system with off shore companies (granted it is getting harder for the past decade)

Or was I unaware the widespread loophole back in the old days?

Not so much a loophole, but back in the 50s all kinds of income were treated the same which meant you could write off your income against your investment losses.

I think it's naive to assume that rich Americans back then weren't working the system. If it was so great, why do we tax different kinds of income differently now?

I have always believed that the majority of the complexity in the tax code is derived from lobbying by special interests to lower taxes on their specific sort of income.

Lately though it seems like tax filing companies have been the ones primarily responsible for sustaining the complexity of the tax code - though whenever someone's particular benefit comes up that group tends to get pretty vocal (i.e. exemptions for SALT taxes and home owner/child credits)