That's not a free market economy.
"it doesn't seem like America has anywhere near enough regulations to be considered true capitalism."
You can't regulate your way into capitalism because capitalism by definition means markets free from government interference. The more it interferes the less capitalism you have.
United Healthcare is a great example. The governments enforce these companies being a monopoly be restricting which companies can operate in which states, having an enormous amount of red tape and regulation, documentation laws, etc.
If it was truly "capitalism" the government wouldn't' get involved at all. Part of the reason that doctors are so expensive to see is because there is a board that the US Government certifies to allow them to control which hospitals are allowed to be teaching hospitals for doctors.
If it was true capitalism there would be no regulation there and any college could graduate doctors. This artificially keeps the supply lower than it would be. These are facts.
My dude, you're acting like Federal government is the only government that matters. It's a common mistake, but in this context it's fatal to your argument.
It's fatal because federal spending is the least relevant kind, since so much of it (and so much of its growth) is for the military, and military spending indicates very little about whether a country is socialist or capitalist on the inside.
In contrast, state/local taxes and programs are--even today--still a majority of the spending that actually tells us anything useful for a socialist/capitalist spectrum, the stuff that involves schools, libraries, policing, homelessness, property rights, etc.
So clearly you are pretty uninformed as the military spending is only 13% of the federal budget. Social Security (AKA a socialist program, IDK if anyone can deny that) is 22%, Medicare (another socialist program is 14.2%). Interest on our prior spending (a lot of it from SS and Medicare, etc, some military too. is 14%
So, if you add social programs you has (SS = 22.5%, Medicare = 14.2%, not counting education) that is 36% of the budget or nearly 3x miltitary spending.
A capitalist economy would NOT have those things are as they are not free market at all, they are the government forcing your to pay into them.
This is another aspect where your thesis is not-fully-baked. If you want people to receive what you meant, you have to stop writing it wrong.
1. You spoke about "the federal tax rate" and claimed it was "0" in 1900.
2. The most charitable interpretation of that is that you meant to say income tax: That's usually what people mean when they're too-vague; It would literally be $0 before it was introduced in 1913; You can't have meant all taxes because those were absolutely >0 and you wouldn't make that kind of math mistake, right?
3. When critiquing the growth and dominance of the income tax, that excludes the separate taxes (payroll) that go to SS/Medicare.
> capitalist economy
I'm not taking a stand on the "what the US is" conclusion at this point. What I'm saying is that your argument--how you're getting there--is unsound (can't ignore state/local level) and unclear (which numbers from where).